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	$36.63	3.237%	$37.8157	$37.82	$37.80	$37.80
Purchase #2	$168.91	10.785%	$187.1269	$187.13	$187.15	$187.10
Purchase #3	$113.94	8.748%	$123.9075	$123.91	$123.90	$123.90
Purchase #4	$237.27	3.312%	$245.1284	$245.13	$245.15	$245.10
Purchase #5	$29.78	13.238%	$33.7223	$33.72	$33.70	$33.70
Purchase #6	$48.61	12.496%	$54.6843	$54.68	$54.70	$54.70
Purchase #7	$137.49	11.383%	$153.1405	$153.14	$153.15	$153.10
7 purchase totals =	$772.63		$835.5256	$835.53	$835.55	$835.40