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	$242.57	3.664%	$251.4578	$251.46	$251.45	$251.50
Purchase #2	$78.54	9.329%	$85.867	$85.87	$85.85	$85.90
Purchase #3	$146.94	12.817%	$165.7733	$165.77	$165.75	$165.80
Purchase #4	$32.78	12.229%	$36.7887	$36.79	$36.80	$36.80
Purchase #5	$72.62	8.560%	$78.8363	$78.84	$78.85	$78.80
Purchase #6	$203.27	8.479%	$220.5053	$220.51	$220.50	$220.50
Purchase #7	$180.60	12.788%	$203.6951	$203.70	$203.70	$203.70
7 purchase totals =	$957.32		$1,042.9235	$1,042.94	$1,042.90	$1,043.00