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	$223.33	12.509%	$251.2663	$251.27	$251.25	$251.30
Purchase #2	$196.29	4.352%	$204.8325	$204.83	$204.85	$204.80
Purchase #3	$196.53	3.381%	$203.1747	$203.17	$203.15	$203.20
Purchase #4	$242.27	12.214%	$271.8609	$271.86	$271.85	$271.90
Purchase #5	$206.37	9.474%	$225.9215	$225.92	$225.90	$225.90
Purchase #6	$151.29	5.189%	$159.1404	$159.14	$159.15	$159.10
Purchase #7	$82.46	7.563%	$88.6964	$88.70	$88.70	$88.70
7 purchase totals =	$1,298.54		$1,404.8927	$1,404.89	$1,404.85	$1,404.90