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	$123.41	5.728%	$130.4789	$130.48	$130.50	$130.50
Purchase #2	$42.78	9.370%	$46.7885	$46.79	$46.80	$46.80
Purchase #3	$15.56	6.157%	$16.518	$16.52	$16.50	$16.50
Purchase #4	$116.63	9.178%	$127.3343	$127.33	$127.35	$127.30
Purchase #5	$139.33	8.683%	$151.428	$151.43	$151.45	$151.40
Purchase #6	$18.59	13.238%	$21.0509	$21.05	$21.05	$21.10
Purchase #7	$171.41	3.562%	$177.5156	$177.52	$177.50	$177.50
7 purchase totals =	$627.71		$671.1142	$671.12	$671.15	$671.10