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	$131.30	6.289%	$139.5575	$139.56	$139.55	$139.60
Purchase #2	$40.31	12.191%	$45.2242	$45.22	$45.20	$45.20
Purchase #3	$29.30	7.207%	$31.4117	$31.41	$31.40	$31.40
Purchase #4	$148.53	4.679%	$155.4797	$155.48	$155.50	$155.50
Purchase #5	$63.79	11.736%	$71.2764	$71.28	$71.30	$71.30
Purchase #6	$221.44	12.567%	$249.2684	$249.27	$249.25	$249.30
Purchase #7	$37.53	6.231%	$39.8685	$39.87	$39.85	$39.90
7 purchase totals =	$672.20		$732.0864	$732.09	$732.05	$732.20