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	$17.77	3.192%	$18.3372	$18.34	$18.35	$18.30
Purchase #2	$236.67	11.318%	$263.4563	$263.46	$263.45	$263.50
Purchase #3	$157.29	10.539%	$173.8668	$173.87	$173.85	$173.90
Purchase #4	$123.85	7.111%	$132.657	$132.66	$132.65	$132.70
Purchase #5	$175.33	4.310%	$182.8867	$182.89	$182.90	$182.90
Purchase #6	$10.52	9.871%	$11.5584	$11.56	$11.55	$11.60
Purchase #7	$111.57	11.176%	$124.0391	$124.04	$124.05	$124.00
7 purchase totals =	$833.00		$906.8015	$906.82	$906.80	$906.90