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	$75.55	3.393%	$78.1134	$78.11	$78.10	$78.10
Purchase #2	$13.68	5.197%	$14.3909	$14.39	$14.40	$14.40
Purchase #3	$167.42	13.266%	$189.6299	$189.63	$189.65	$189.60
Purchase #4	$250.51	6.122%	$265.8462	$265.85	$265.85	$265.80
Purchase #5	$156.75	12.869%	$176.9222	$176.92	$176.90	$176.90
Purchase #6	$81.82	10.579%	$90.4757	$90.48	$90.50	$90.50
Purchase #7	$21.75	4.672%	$22.7662	$22.77	$22.75	$22.80
7 purchase totals =	$767.48		$838.1445	$838.15	$838.15	$838.10