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	$57.60	11.335%	$64.129	$64.13	$64.15	$64.10
Purchase #2	$204.85	10.732%	$226.8345	$226.83	$226.85	$226.80
Purchase #3	$112.94	10.592%	$124.9026	$124.90	$124.90	$124.90
Purchase #4	$93.28	6.823%	$99.6445	$99.64	$99.65	$99.60
Purchase #5	$120.54	6.610%	$128.5077	$128.51	$128.50	$128.50
Purchase #6	$164.27	12.294%	$184.4654	$184.47	$184.45	$184.50
Purchase #7	$11.93	11.760%	$13.333	$13.33	$13.35	$13.30
7 purchase totals =	$765.41		$841.8167	$841.81	$841.85	$841.70