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	$231.85	13.700%	$263.6135	$263.61	$263.60	$263.60
Purchase #2	$113.52	6.426%	$120.8148	$120.81	$120.80	$120.80
Purchase #3	$149.77	8.539%	$162.5589	$162.56	$162.55	$162.60
Purchase #4	$45.74	6.202%	$48.5768	$48.58	$48.60	$48.60
Purchase #5	$43.76	4.343%	$45.6605	$45.66	$45.65	$45.70
Purchase #6	$62.89	4.290%	$65.588	$65.59	$65.60	$65.60
Purchase #7	$155.41	6.577%	$165.6313	$165.63	$165.65	$165.60
7 purchase totals =	$802.94		$872.4438	$872.44	$872.45	$872.50