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	$161.72	11.149%	$179.7502	$179.75	$179.75	$179.80
Purchase #2	$25.73	10.785%	$28.505	$28.51	$28.50	$28.50
Purchase #3	$39.90	7.315%	$42.8187	$42.82	$42.80	$42.80
Purchase #4	$246.88	10.505%	$272.8147	$272.81	$272.80	$272.80
Purchase #5	$25.43	13.731%	$28.9218	$28.92	$28.90	$28.90
Purchase #6	$250.51	8.674%	$272.2392	$272.24	$272.25	$272.20
Purchase #7	$63.41	12.850%	$71.5582	$71.56	$71.55	$71.60
7 purchase totals =	$813.58		$896.6078	$896.61	$896.55	$896.60