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	$101.85	9.121%	$111.1397	$111.14	$111.15	$111.10
Purchase #2	$150.51	13.146%	$170.296	$170.30	$170.30	$170.30
Purchase #3	$120.72	10.760%	$133.7095	$133.71	$133.70	$133.70
Purchase #4	$97.92	13.302%	$110.9453	$110.95	$110.95	$110.90
Purchase #5	$100.72	4.552%	$105.3048	$105.30	$105.30	$105.30
Purchase #6	$231.62	8.477%	$251.2544	$251.25	$251.25	$251.30
Purchase #7	$88.66	12.690%	$99.911	$99.91	$99.90	$99.90
7 purchase totals =	$892.00		$982.5607	$982.56	$982.55	$982.50