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	$85.33	7.336%	$91.5898	$91.59	$91.60	$91.60
Purchase #2	$32.81	8.863%	$35.718	$35.72	$35.70	$35.70
Purchase #3	$21.38	6.732%	$22.8193	$22.82	$22.80	$22.80
Purchase #4	$208.54	9.489%	$228.3284	$228.33	$228.35	$228.30
Purchase #5	$83.57	9.556%	$91.5559	$91.56	$91.55	$91.60
Purchase #6	$250.70	10.614%	$277.3093	$277.31	$277.30	$277.30
Purchase #7	$165.30	4.556%	$172.8311	$172.83	$172.85	$172.80
7 purchase totals =	$847.63		$920.1518	$920.16	$920.15	$920.10