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	$227.70	13.191%	$257.7359	$257.74	$257.75	$257.70
Purchase #2	$210.42	5.530%	$222.0562	$222.06	$222.05	$222.10
Purchase #3	$28.52	10.259%	$31.4459	$31.45	$31.45	$31.40
Purchase #4	$87.26	11.612%	$97.3926	$97.39	$97.40	$97.40
Purchase #5	$89.31	12.498%	$100.472	$100.47	$100.45	$100.50
Purchase #6	$42.50	7.735%	$45.7874	$45.79	$45.80	$45.80
Purchase #7	$176.51	6.766%	$188.4527	$188.45	$188.45	$188.50
7 purchase totals =	$862.22		$943.3427	$943.35	$943.35	$943.40