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	$203.52	4.578%	$212.8371	$212.84	$212.85	$212.80
Purchase #2	$49.90	4.526%	$52.1585	$52.16	$52.15	$52.20
Purchase #3	$72.51	6.814%	$77.4508	$77.45	$77.45	$77.50
Purchase #4	$235.25	3.383%	$243.2085	$243.21	$243.20	$243.20
Purchase #5	$45.87	10.549%	$50.7088	$50.71	$50.70	$50.70
Purchase #6	$59.63	13.158%	$67.4761	$67.48	$67.50	$67.50
Purchase #7	$137.89	9.600%	$151.1274	$151.13	$151.15	$151.10
7 purchase totals =	$804.57		$854.9672	$854.98	$855.00	$855.00