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	$134.61	3.816%	$139.7467	$139.75	$139.75	$139.70
Purchase #2	$32.90	12.672%	$37.0691	$37.07	$37.05	$37.10
Purchase #3	$83.83	5.470%	$88.4155	$88.42	$88.40	$88.40
Purchase #4	$171.47	12.469%	$192.8506	$192.85	$192.85	$192.90
Purchase #5	$113.91	9.828%	$125.1051	$125.11	$125.10	$125.10
Purchase #6	$109.39	13.318%	$123.9586	$123.96	$123.95	$124.00
Purchase #7	$18.70	9.766%	$20.5262	$20.53	$20.55	$20.50
7 purchase totals =	$664.81		$727.6718	$727.69	$727.65	$727.70