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	$123.94	12.353%	$139.2503	$139.25	$139.25	$139.30
Purchase #2	$112.90	4.363%	$117.8258	$117.83	$117.85	$117.80
Purchase #3	$209.29	4.246%	$218.1765	$218.18	$218.20	$218.20
Purchase #4	$247.47	4.525%	$258.668	$258.67	$258.65	$258.70
Purchase #5	$48.53	12.343%	$54.5201	$54.52	$54.50	$54.50
Purchase #6	$56.76	11.390%	$63.225	$63.23	$63.25	$63.20
Purchase #7	$154.53	6.843%	$165.1045	$165.10	$165.10	$165.10
7 purchase totals =	$953.42		$1,016.7702	$1,016.78	$1,016.80	$1,016.80