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	$109.43	12.563%	$123.1777	$123.18	$123.20	$123.20
Purchase #2	$115.89	13.764%	$131.8411	$131.84	$131.85	$131.80
Purchase #3	$165.76	13.614%	$188.3266	$188.33	$188.35	$188.30
Purchase #4	$34.37	9.872%	$37.763	$37.76	$37.75	$37.80
Purchase #5	$220.53	4.814%	$231.1463	$231.15	$231.15	$231.10
Purchase #6	$74.72	3.785%	$77.5482	$77.55	$77.55	$77.50
Purchase #7	$222.95	8.161%	$241.1449	$241.14	$241.15	$241.10
7 purchase totals =	$943.65		$1,030.9478	$1,030.95	$1,031.00	$1,030.80