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	$101.63	6.595%	$108.3325	$108.33	$108.35	$108.30
Purchase #2	$230.73	5.255%	$242.8549	$242.85	$242.85	$242.90
Purchase #3	$97.28	11.136%	$108.1131	$108.11	$108.10	$108.10
Purchase #4	$90.43	3.164%	$93.2912	$93.29	$93.30	$93.30
Purchase #5	$228.35	4.505%	$238.6372	$238.64	$238.65	$238.60
Purchase #6	$36.48	7.559%	$39.2375	$39.24	$39.25	$39.20
Purchase #7	$90.34	9.717%	$99.1183	$99.12	$99.10	$99.10
7 purchase totals =	$875.24		$929.5847	$929.58	$929.60	$929.50