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	$99.39	12.604%	$111.9171	$111.92	$111.90	$111.90
Purchase #2	$23.53	11.853%	$26.319	$26.32	$26.30	$26.30
Purchase #3	$11.86	3.297%	$12.251	$12.25	$12.25	$12.30
Purchase #4	$146.85	9.447%	$160.7229	$160.72	$160.70	$160.70
Purchase #5	$94.88	3.762%	$98.4494	$98.45	$98.45	$98.40
Purchase #6	$136.58	9.431%	$149.4609	$149.46	$149.45	$149.50
Purchase #7	$28.72	13.315%	$32.5441	$32.54	$32.55	$32.50
7 purchase totals =	$541.81		$591.6644	$591.66	$591.60	$591.60