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	$139.89	5.196%	$147.1587	$147.16	$147.15	$147.20
Purchase #2	$152.32	3.756%	$158.0411	$158.04	$158.05	$158.00
Purchase #3	$221.90	6.566%	$236.47	$236.47	$236.45	$236.50
Purchase #4	$157.86	8.700%	$171.5938	$171.59	$171.60	$171.60
Purchase #5	$209.44	11.505%	$233.5361	$233.54	$233.55	$233.50
Purchase #6	$137.58	4.382%	$143.6088	$143.61	$143.60	$143.60
Purchase #7	$16.41	6.699%	$17.5093	$17.51	$17.50	$17.50
7 purchase totals =	$1,035.40		$1,107.9178	$1,107.92	$1,107.90	$1,107.90