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	$171.81	11.259%	$191.1541	$191.15	$191.15	$191.20
Purchase #2	$78.98	13.401%	$89.5641	$89.56	$89.55	$89.60
Purchase #3	$144.84	5.171%	$152.3297	$152.33	$152.35	$152.30
Purchase #4	$116.69	4.782%	$122.2701	$122.27	$122.25	$122.30
Purchase #5	$159.33	12.391%	$179.0726	$179.07	$179.05	$179.10
Purchase #6	$34.92	8.411%	$37.8571	$37.86	$37.85	$37.90
Purchase #7	$68.98	3.346%	$71.2881	$71.29	$71.30	$71.30
7 purchase totals =	$775.55		$843.5358	$843.53	$843.50	$843.70