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	$243.85	12.834%	$275.1457	$275.15	$275.15	$275.10
Purchase #2	$146.31	9.244%	$159.8349	$159.83	$159.85	$159.80
Purchase #3	$133.82	12.331%	$150.3213	$150.32	$150.30	$150.30
Purchase #4	$125.63	9.430%	$137.4769	$137.48	$137.50	$137.50
Purchase #5	$221.52	12.781%	$249.8325	$249.83	$249.85	$249.80
Purchase #6	$52.84	8.420%	$57.2891	$57.29	$57.30	$57.30
Purchase #7	$7.49	4.513%	$7.828	$7.83	$7.85	$7.80
7 purchase totals =	$931.46		$1,037.7284	$1,037.73	$1,037.80	$1,037.60