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	$141.29	3.267%	$145.9059	$145.91	$145.90	$145.90
Purchase #2	$114.64	5.357%	$120.7813	$120.78	$120.80	$120.80
Purchase #3	$81.34	4.702%	$85.1646	$85.16	$85.15	$85.20
Purchase #4	$185.27	8.730%	$201.4441	$201.44	$201.45	$201.40
Purchase #5	$48.98	11.217%	$54.4741	$54.47	$54.45	$54.50
Purchase #6	$9.96	5.834%	$10.5411	$10.54	$10.55	$10.50
Purchase #7	$50.32	8.332%	$54.5127	$54.51	$54.50	$54.50
7 purchase totals =	$631.80		$672.8238	$672.81	$672.80	$672.80