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	$37.75	6.489%	$40.1996	$40.20	$40.20	$40.20
Purchase #2	$77.43	7.652%	$83.3549	$83.35	$83.35	$83.40
Purchase #3	$87.53	13.841%	$99.645	$99.65	$99.65	$99.60
Purchase #4	$196.27	9.153%	$214.2346	$214.23	$214.25	$214.20
Purchase #5	$33.64	10.310%	$37.1083	$37.11	$37.10	$37.10
Purchase #6	$52.93	3.588%	$54.8291	$54.83	$54.85	$54.80
Purchase #7	$209.76	10.510%	$231.8058	$231.81	$231.80	$231.80
7 purchase totals =	$695.31		$761.1773	$761.18	$761.20	$761.10