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	$178.80	6.117%	$189.7372	$189.74	$189.75	$189.70
Purchase #2	$88.51	5.600%	$93.4666	$93.47	$93.45	$93.50
Purchase #3	$125.90	4.748%	$131.8777	$131.88	$131.90	$131.90
Purchase #4	$76.81	6.870%	$82.0868	$82.09	$82.10	$82.10
Purchase #5	$100.34	10.846%	$111.2229	$111.22	$111.20	$111.20
Purchase #6	$151.78	13.837%	$172.7818	$172.78	$172.80	$172.80
Purchase #7	$13.43	6.470%	$14.2989	$14.30	$14.30	$14.30
7 purchase totals =	$735.57		$795.4719	$795.48	$795.50	$795.50