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	$141.27	11.511%	$157.5316	$157.53	$157.55	$157.50
Purchase #2	$45.76	5.396%	$48.2292	$48.23	$48.25	$48.20
Purchase #3	$30.67	13.628%	$34.8497	$34.85	$34.85	$34.80
Purchase #4	$89.77	11.447%	$100.046	$100.05	$100.05	$100.00
Purchase #5	$45.59	12.165%	$51.136	$51.14	$51.15	$51.10
Purchase #6	$28.67	3.554%	$29.6889	$29.69	$29.70	$29.70
Purchase #7	$127.35	8.313%	$137.9366	$137.94	$137.95	$137.90
7 purchase totals =	$509.08		$559.4180	$559.43	$559.50	$559.20