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	$241.33	3.207%	$249.0695	$249.07	$249.05	$249.10
Purchase #2	$53.66	11.580%	$59.8738	$59.87	$59.85	$59.90
Purchase #3	$215.56	7.308%	$231.3131	$231.31	$231.30	$231.30
Purchase #4	$42.43	8.248%	$45.9296	$45.93	$45.95	$45.90
Purchase #5	$18.72	12.628%	$21.084	$21.08	$21.10	$21.10
Purchase #6	$223.44	13.374%	$253.3229	$253.32	$253.30	$253.30
Purchase #7	$90.37	11.350%	$100.627	$100.63	$100.65	$100.60
7 purchase totals =	$885.51		$961.2199	$961.21	$961.20	$961.20