Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$172.31	6.299%	$183.1638	$183.16	$183.15	$183.20
Purchase #2	$198.27	9.354%	$216.8162	$216.82	$216.80	$216.80
Purchase #3	$74.89	7.231%	$80.3053	$80.31	$80.30	$80.30
Purchase #4	$152.69	12.333%	$171.5213	$171.52	$171.50	$171.50
Purchase #5	$169.39	7.112%	$181.437	$181.44	$181.45	$181.40
Purchase #6	$80.46	8.215%	$87.0698	$87.07	$87.05	$87.10
Purchase #7	$174.77	3.237%	$180.4273	$180.43	$180.45	$180.40
7 purchase totals =	$1,022.78		$1,100.7407	$1,100.75	$1,100.70	$1,100.70