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	$222.48	10.285%	$245.3621	$245.36	$245.35	$245.40
Purchase #2	$63.30	5.203%	$66.5935	$66.59	$66.60	$66.60
Purchase #3	$55.55	13.733%	$63.1787	$63.18	$63.20	$63.20
Purchase #4	$169.71	9.530%	$185.8834	$185.88	$185.90	$185.90
Purchase #5	$74.97	4.148%	$78.0798	$78.08	$78.10	$78.10
Purchase #6	$124.78	13.730%	$141.9123	$141.91	$141.90	$141.90
Purchase #7	$105.25	7.467%	$113.109	$113.11	$113.10	$113.10
7 purchase totals =	$816.04		$894.1188	$894.11	$894.15	$894.20