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	$223.82	12.568%	$251.9497	$251.95	$251.95	$251.90
Purchase #2	$120.68	7.566%	$129.8106	$129.81	$129.80	$129.80
Purchase #3	$17.32	3.318%	$17.8947	$17.89	$17.90	$17.90
Purchase #4	$242.83	8.505%	$263.4827	$263.48	$263.50	$263.50
Purchase #5	$60.52	12.168%	$67.8841	$67.88	$67.90	$67.90
Purchase #6	$41.60	8.700%	$45.2192	$45.22	$45.20	$45.20
Purchase #7	$63.90	11.468%	$71.2281	$71.23	$71.25	$71.20
7 purchase totals =	$770.67		$847.4691	$847.46	$847.50	$847.40