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	$7.35	12.269%	$8.2518	$8.25	$8.25	$8.30
Purchase #2	$82.37	8.525%	$89.392	$89.39	$89.40	$89.40
Purchase #3	$174.31	11.162%	$193.7665	$193.77	$193.75	$193.80
Purchase #4	$60.59	8.620%	$65.8129	$65.81	$65.80	$65.80
Purchase #5	$30.61	9.158%	$33.4133	$33.41	$33.40	$33.40
Purchase #6	$57.73	10.154%	$63.5919	$63.59	$63.60	$63.60
Purchase #7	$158.35	11.325%	$176.2831	$176.28	$176.30	$176.30
7 purchase totals =	$571.31		$630.5115	$630.50	$630.50	$630.60