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	$108.33	4.549%	$113.2579	$113.26	$113.25	$113.30
Purchase #2	$209.72	6.109%	$222.5318	$222.53	$222.55	$222.50
Purchase #3	$129.31	8.581%	$140.4061	$140.41	$140.40	$140.40
Purchase #4	$196.96	12.343%	$221.2708	$221.27	$221.25	$221.30
Purchase #5	$41.62	9.717%	$45.6642	$45.66	$45.65	$45.70
Purchase #6	$221.25	13.191%	$250.4351	$250.44	$250.45	$250.40
Purchase #7	$81.66	7.282%	$87.6065	$87.61	$87.60	$87.60
7 purchase totals =	$988.85		$1,081.1724	$1,081.18	$1,081.15	$1,081.20