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	$31.39	5.261%	$33.0414	$33.04	$33.05	$33.00
Purchase #2	$81.42	11.611%	$90.8737	$90.87	$90.85	$90.90
Purchase #3	$146.41	6.171%	$155.445	$155.45	$155.45	$155.40
Purchase #4	$155.77	6.825%	$166.4013	$166.40	$166.40	$166.40
Purchase #5	$125.51	11.423%	$139.847	$139.85	$139.85	$139.80
Purchase #6	$54.84	7.846%	$59.1427	$59.14	$59.15	$59.10
Purchase #7	$180.65	9.283%	$197.4197	$197.42	$197.40	$197.40
7 purchase totals =	$775.99		$842.1708	$842.17	$842.15	$842.00