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	$121.86	8.414%	$132.1133	$132.11	$132.10	$132.10
Purchase #2	$90.61	7.111%	$97.0533	$97.05	$97.05	$97.10
Purchase #3	$138.76	5.223%	$146.0074	$146.01	$146.00	$146.00
Purchase #4	$53.37	12.261%	$59.9137	$59.91	$59.90	$59.90
Purchase #5	$228.80	11.419%	$254.9267	$254.93	$254.95	$254.90
Purchase #6	$122.94	12.137%	$137.8612	$137.86	$137.85	$137.90
Purchase #7	$77.62	13.791%	$88.3246	$88.32	$88.30	$88.30
7 purchase totals =	$833.96		$916.2002	$916.19	$916.15	$916.20