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	$45.57	11.680%	$50.8926	$50.89	$50.90	$50.90
Purchase #2	$66.29	9.154%	$72.3582	$72.36	$72.35	$72.40
Purchase #3	$237.33	3.176%	$244.8676	$244.87	$244.85	$244.90
Purchase #4	$155.77	6.184%	$165.4028	$165.40	$165.40	$165.40
Purchase #5	$189.58	10.190%	$208.8982	$208.90	$208.90	$208.90
Purchase #6	$35.78	6.512%	$38.11	$38.11	$38.10	$38.10
Purchase #7	$28.58	13.449%	$32.4237	$32.42	$32.40	$32.40
7 purchase totals =	$758.90		$812.9531	$812.95	$812.90	$813.00