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	$224.79	12.630%	$253.181	$253.18	$253.20	$253.20
Purchase #2	$202.58	11.251%	$225.3723	$225.37	$225.35	$225.40
Purchase #3	$240.86	3.814%	$250.0464	$250.05	$250.05	$250.00
Purchase #4	$85.92	3.782%	$89.1695	$89.17	$89.15	$89.20
Purchase #5	$29.68	10.203%	$32.7083	$32.71	$32.70	$32.70
Purchase #6	$144.92	7.748%	$156.1484	$156.15	$156.15	$156.10
Purchase #7	$138.80	5.829%	$146.8907	$146.89	$146.90	$146.90
7 purchase totals =	$1,067.55		$1,153.5166	$1,153.52	$1,153.50	$1,153.50