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	$177.72	4.406%	$185.5503	$185.55	$185.55	$185.60
Purchase #2	$26.61	7.249%	$28.539	$28.54	$28.55	$28.50
Purchase #3	$111.33	8.545%	$120.8431	$120.84	$120.85	$120.80
Purchase #4	$160.72	12.209%	$180.3423	$180.34	$180.35	$180.30
Purchase #5	$226.36	5.454%	$238.7057	$238.71	$238.70	$238.70
Purchase #6	$44.81	11.698%	$50.0519	$50.05	$50.05	$50.10
Purchase #7	$33.40	13.513%	$37.9133	$37.91	$37.90	$37.90
7 purchase totals =	$780.95		$841.9456	$841.94	$841.95	$841.90