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	$145.47	9.375%	$159.1078	$159.11	$159.10	$159.10
Purchase #2	$42.45	6.586%	$45.2458	$45.25	$45.25	$45.20
Purchase #3	$130.27	8.850%	$141.7989	$141.80	$141.80	$141.80
Purchase #4	$243.34	8.215%	$263.3304	$263.33	$263.35	$263.30
Purchase #5	$78.30	5.298%	$82.4483	$82.45	$82.45	$82.40
Purchase #6	$133.72	7.849%	$144.2157	$144.22	$144.20	$144.20
Purchase #7	$28.93	6.449%	$30.7957	$30.80	$30.80	$30.80
7 purchase totals =	$802.48		$866.9426	$866.96	$866.95	$866.80