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	$71.38	9.459%	$78.1318	$78.13	$78.15	$78.10
Purchase #2	$72.25	3.588%	$74.8423	$74.84	$74.85	$74.80
Purchase #3	$209.32	13.785%	$238.1748	$238.17	$238.15	$238.20
Purchase #4	$124.83	4.576%	$130.5422	$130.54	$130.55	$130.50
Purchase #5	$174.74	12.515%	$196.6087	$196.61	$196.60	$196.60
Purchase #6	$23.94	12.762%	$26.9952	$27.00	$27.00	$27.00
Purchase #7	$188.91	4.576%	$197.5545	$197.55	$197.55	$197.60
7 purchase totals =	$865.37		$942.8495	$942.84	$942.85	$942.80