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	$49.91	11.614%	$55.7065	$55.71	$55.70	$55.70
Purchase #2	$205.60	5.140%	$216.1678	$216.17	$216.15	$216.20
Purchase #3	$18.77	12.404%	$21.0982	$21.10	$21.10	$21.10
Purchase #4	$20.46	3.339%	$21.1432	$21.14	$21.15	$21.10
Purchase #5	$159.56	10.626%	$176.5148	$176.51	$176.50	$176.50
Purchase #6	$148.46	6.116%	$157.5398	$157.54	$157.55	$157.50
Purchase #7	$116.89	13.221%	$132.344	$132.34	$132.35	$132.30
7 purchase totals =	$719.65		$780.5143	$780.51	$780.50	$780.40