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	$114.96	8.304%	$124.5063	$124.51	$124.50	$124.50
Purchase #2	$198.82	13.251%	$225.1656	$225.17	$225.15	$225.20
Purchase #3	$145.98	3.514%	$151.1097	$151.11	$151.10	$151.10
Purchase #4	$42.33	12.433%	$47.5929	$47.59	$47.60	$47.60
Purchase #5	$45.58	12.529%	$51.2907	$51.29	$51.30	$51.30
Purchase #6	$233.50	4.572%	$244.1756	$244.18	$244.20	$244.20
Purchase #7	$18.58	7.673%	$20.0056	$20.01	$20.00	$20.00
7 purchase totals =	$799.75		$863.8464	$863.86	$863.85	$863.90