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	$159.40	12.330%	$179.054	$179.05	$179.05	$179.10
Purchase #2	$146.79	13.642%	$166.8151	$166.82	$166.80	$166.80
Purchase #3	$57.54	5.681%	$60.8088	$60.81	$60.80	$60.80
Purchase #4	$40.28	4.352%	$42.033	$42.03	$42.05	$42.00
Purchase #5	$188.27	12.637%	$212.0617	$212.06	$212.05	$212.10
Purchase #6	$227.50	12.185%	$255.2209	$255.22	$255.20	$255.20
Purchase #7	$29.49	9.554%	$32.3075	$32.31	$32.30	$32.30
7 purchase totals =	$849.27		$948.3010	$948.30	$948.25	$948.30