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	$25.66	12.375%	$28.8354	$28.84	$28.85	$28.80
Purchase #2	$135.86	11.279%	$151.1836	$151.18	$151.20	$151.20
Purchase #3	$242.82	4.772%	$254.4074	$254.41	$254.40	$254.40
Purchase #4	$36.52	9.819%	$40.1059	$40.11	$40.10	$40.10
Purchase #5	$102.80	8.110%	$111.1371	$111.14	$111.15	$111.10
Purchase #6	$79.96	12.738%	$90.1453	$90.15	$90.15	$90.10
Purchase #7	$150.63	10.381%	$166.2669	$166.27	$166.25	$166.30
7 purchase totals =	$774.25		$842.0816	$842.10	$842.10	$842.00