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	$239.58	7.186%	$256.7962	$256.80	$256.80	$256.80
Purchase #2	$40.44	5.185%	$42.5368	$42.54	$42.55	$42.50
Purchase #3	$30.89	7.489%	$33.2034	$33.20	$33.20	$33.20
Purchase #4	$167.69	6.693%	$178.9135	$178.91	$178.90	$178.90
Purchase #5	$163.34	11.486%	$182.1012	$182.10	$182.10	$182.10
Purchase #6	$37.46	9.700%	$41.0936	$41.09	$41.10	$41.10
Purchase #7	$58.69	10.845%	$65.0549	$65.05	$65.05	$65.10
7 purchase totals =	$738.09		$799.6996	$799.69	$799.70	$799.70