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	$190.74	4.384%	$199.102	$199.10	$199.10	$199.10
Purchase #2	$167.72	4.113%	$174.6183	$174.62	$174.60	$174.60
Purchase #3	$19.62	6.840%	$20.962	$20.96	$20.95	$21.00
Purchase #4	$80.42	12.267%	$90.2851	$90.29	$90.30	$90.30
Purchase #5	$133.89	6.344%	$142.384	$142.38	$142.40	$142.40
Purchase #6	$46.86	11.345%	$52.1763	$52.18	$52.20	$52.20
Purchase #7	$139.56	3.707%	$144.7335	$144.73	$144.75	$144.70
7 purchase totals =	$778.81		$824.2612	$824.26	$824.30	$824.30