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	$216.69	12.320%	$243.3862	$243.39	$243.40	$243.40
Purchase #2	$65.78	6.493%	$70.0511	$70.05	$70.05	$70.10
Purchase #3	$151.47	7.157%	$162.3107	$162.31	$162.30	$162.30
Purchase #4	$185.30	12.546%	$208.5477	$208.55	$208.55	$208.50
Purchase #5	$67.30	8.497%	$73.0185	$73.02	$73.00	$73.00
Purchase #6	$29.51	5.137%	$31.0259	$31.03	$31.05	$31.00
Purchase #7	$32.28	4.105%	$33.6051	$33.61	$33.60	$33.60
7 purchase totals =	$748.33		$821.9452	$821.96	$821.95	$821.90