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	$64.30	12.105%	$72.0835	$72.08	$72.10	$72.10
Purchase #2	$218.95	11.869%	$244.9372	$244.94	$244.95	$244.90
Purchase #3	$83.65	13.133%	$94.6358	$94.64	$94.65	$94.60
Purchase #4	$40.38	12.594%	$45.4655	$45.47	$45.45	$45.50
Purchase #5	$77.91	7.187%	$83.5094	$83.51	$83.50	$83.50
Purchase #6	$197.46	9.385%	$215.9916	$215.99	$216.00	$216.00
Purchase #7	$22.39	7.455%	$24.0592	$24.06	$24.05	$24.10
7 purchase totals =	$705.04		$780.6822	$780.69	$780.70	$780.70