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	$128.98	13.110%	$145.8893	$145.89	$145.90	$145.90
Purchase #2	$231.44	5.710%	$244.6552	$244.66	$244.65	$244.70
Purchase #3	$138.84	3.302%	$143.4245	$143.42	$143.40	$143.40
Purchase #4	$70.81	6.388%	$75.3333	$75.33	$75.35	$75.30
Purchase #5	$136.83	8.401%	$148.3251	$148.33	$148.35	$148.30
Purchase #6	$165.77	8.661%	$180.1273	$180.13	$180.15	$180.10
Purchase #7	$36.87	10.385%	$40.6989	$40.70	$40.70	$40.70
7 purchase totals =	$909.54		$978.4536	$978.46	$978.50	$978.40