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	$123.81	3.640%	$128.3167	$128.32	$128.30	$128.30
Purchase #2	$28.83	12.363%	$32.3943	$32.39	$32.40	$32.40
Purchase #3	$238.87	10.672%	$264.3622	$264.36	$264.35	$264.40
Purchase #4	$230.45	10.167%	$253.8799	$253.88	$253.90	$253.90
Purchase #5	$198.39	12.358%	$222.907	$222.91	$222.90	$222.90
Purchase #6	$54.55	10.631%	$60.3492	$60.35	$60.35	$60.30
Purchase #7	$137.85	8.426%	$149.4652	$149.47	$149.45	$149.50
7 purchase totals =	$1,012.75		$1,111.6745	$1,111.68	$1,111.65	$1,111.70