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	$190.43	7.505%	$204.7218	$204.72	$204.70	$204.70
Purchase #2	$37.62	12.586%	$42.3549	$42.35	$42.35	$42.40
Purchase #3	$125.83	9.530%	$137.8216	$137.82	$137.80	$137.80
Purchase #4	$215.58	8.324%	$233.5249	$233.52	$233.50	$233.50
Purchase #5	$28.43	3.763%	$29.4998	$29.50	$29.50	$29.50
Purchase #6	$205.59	10.642%	$227.4689	$227.47	$227.45	$227.50
Purchase #7	$97.92	6.698%	$104.4787	$104.48	$104.50	$104.50
7 purchase totals =	$901.40		$979.8706	$979.86	$979.80	$979.90