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	$110.62	5.138%	$116.3037	$116.30	$116.30	$116.30
Purchase #2	$34.59	8.687%	$37.5948	$37.59	$37.60	$37.60
Purchase #3	$118.25	10.392%	$130.5385	$130.54	$130.55	$130.50
Purchase #4	$199.52	6.403%	$212.2953	$212.30	$212.30	$212.30
Purchase #5	$37.78	11.552%	$42.1443	$42.14	$42.15	$42.10
Purchase #6	$172.50	11.113%	$191.6699	$191.67	$191.65	$191.70
Purchase #7	$38.44	10.733%	$42.5658	$42.57	$42.55	$42.60
7 purchase totals =	$711.70		$773.1123	$773.11	$773.10	$773.10