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	$25.31	13.351%	$28.6891	$28.69	$28.70	$28.70
Purchase #2	$213.87	13.271%	$242.2527	$242.25	$242.25	$242.30
Purchase #3	$249.47	6.573%	$265.8677	$265.87	$265.85	$265.90
Purchase #4	$70.81	3.316%	$73.1581	$73.16	$73.15	$73.20
Purchase #5	$126.78	10.389%	$139.9512	$139.95	$139.95	$140.00
Purchase #6	$123.55	10.325%	$136.3065	$136.31	$136.30	$136.30
Purchase #7	$79.87	12.748%	$90.0518	$90.05	$90.05	$90.10
7 purchase totals =	$889.66		$976.2771	$976.28	$976.25	$976.50