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	$177.94	3.666%	$184.4633	$184.46	$184.45	$184.50
Purchase #2	$133.65	4.242%	$139.3194	$139.32	$139.30	$139.30
Purchase #3	$172.37	13.308%	$195.309	$195.31	$195.30	$195.30
Purchase #4	$167.84	13.485%	$190.4732	$190.47	$190.45	$190.50
Purchase #5	$179.67	4.682%	$188.0821	$188.08	$188.10	$188.10
Purchase #6	$20.62	6.242%	$21.9071	$21.91	$21.90	$21.90
Purchase #7	$78.70	3.286%	$81.2861	$81.29	$81.30	$81.30
7 purchase totals =	$930.79		$1,000.8402	$1,000.84	$1,000.80	$1,000.90