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	$20.33	5.809%	$21.511	$21.51	$21.50	$21.50
Purchase #2	$40.60	4.295%	$42.3438	$42.34	$42.35	$42.30
Purchase #3	$170.55	4.755%	$178.6597	$178.66	$178.65	$178.70
Purchase #4	$132.94	10.528%	$146.9359	$146.94	$146.95	$146.90
Purchase #5	$137.57	10.216%	$151.6242	$151.62	$151.60	$151.60
Purchase #6	$62.56	11.619%	$69.8288	$69.83	$69.85	$69.80
Purchase #7	$196.72	11.775%	$219.8838	$219.88	$219.90	$219.90
7 purchase totals =	$761.27		$830.7872	$830.78	$830.80	$830.70