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	$231.40	8.264%	$250.5229	$250.52	$250.50	$250.50
Purchase #2	$84.41	7.251%	$90.5306	$90.53	$90.55	$90.50
Purchase #3	$30.94	8.306%	$33.5099	$33.51	$33.50	$33.50
Purchase #4	$143.79	6.148%	$152.6302	$152.63	$152.65	$152.60
Purchase #5	$30.86	5.605%	$32.5897	$32.59	$32.60	$32.60
Purchase #6	$37.74	12.685%	$42.5273	$42.53	$42.55	$42.50
Purchase #7	$161.79	5.114%	$170.0639	$170.06	$170.05	$170.10
7 purchase totals =	$720.93		$772.3745	$772.37	$772.40	$772.30