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	$85.44	10.695%	$94.5778	$94.58	$94.60	$94.60
Purchase #2	$157.61	5.844%	$166.8207	$166.82	$166.80	$166.80
Purchase #3	$78.57	11.843%	$87.875	$87.88	$87.90	$87.90
Purchase #4	$40.77	3.430%	$42.1684	$42.17	$42.15	$42.20
Purchase #5	$172.43	4.514%	$180.2135	$180.21	$180.20	$180.20
Purchase #6	$155.89	4.333%	$162.6447	$162.64	$162.65	$162.60
Purchase #7	$222.54	11.552%	$248.2478	$248.25	$248.25	$248.20
7 purchase totals =	$913.25		$982.5479	$982.55	$982.55	$982.50