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	$148.59	11.236%	$165.2856	$165.29	$165.30	$165.30
Purchase #2	$205.45	6.371%	$218.5392	$218.54	$218.55	$218.50
Purchase #3	$48.76	4.180%	$50.7982	$50.80	$50.80	$50.80
Purchase #4	$35.89	11.863%	$40.1476	$40.15	$40.15	$40.10
Purchase #5	$153.72	11.443%	$171.3102	$171.31	$171.30	$171.30
Purchase #6	$37.81	5.633%	$39.9398	$39.94	$39.95	$39.90
Purchase #7	$24.86	7.322%	$26.6802	$26.68	$26.70	$26.70
7 purchase totals =	$655.08		$712.7008	$712.71	$712.75	$712.60