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	$92.59	12.187%	$103.8739	$103.87	$103.85	$103.90
Purchase #2	$97.67	12.175%	$109.5613	$109.56	$109.55	$109.60
Purchase #3	$206.51	7.830%	$222.6797	$222.68	$222.70	$222.70
Purchase #4	$48.26	5.227%	$50.7826	$50.78	$50.80	$50.80
Purchase #5	$178.67	13.803%	$203.3318	$203.33	$203.35	$203.30
Purchase #6	$241.76	11.601%	$269.8066	$269.81	$269.80	$269.80
Purchase #7	$29.28	10.609%	$32.3863	$32.39	$32.40	$32.40
7 purchase totals =	$894.74		$992.4222	$992.42	$992.45	$992.50