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	$245.83	4.589%	$257.1111	$257.11	$257.10	$257.10
Purchase #2	$156.64	10.118%	$172.4888	$172.49	$172.50	$172.50
Purchase #3	$129.54	11.850%	$144.8905	$144.89	$144.90	$144.90
Purchase #4	$31.93	7.229%	$34.2382	$34.24	$34.25	$34.20
Purchase #5	$234.44	4.117%	$244.0919	$244.09	$244.10	$244.10
Purchase #6	$115.83	7.269%	$124.2497	$124.25	$124.25	$124.20
Purchase #7	$37.38	7.186%	$40.0661	$40.07	$40.05	$40.10
7 purchase totals =	$951.59		$1,017.1363	$1,017.14	$1,017.15	$1,017.10