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	$57.33	12.510%	$64.502	$64.50	$64.50	$64.50
Purchase #2	$41.39	7.128%	$44.3403	$44.34	$44.35	$44.30
Purchase #3	$54.92	7.647%	$59.1197	$59.12	$59.10	$59.10
Purchase #4	$231.52	10.705%	$256.3042	$256.30	$256.30	$256.30
Purchase #5	$176.40	10.736%	$195.3383	$195.34	$195.35	$195.30
Purchase #6	$31.69	6.191%	$33.6519	$33.65	$33.65	$33.70
Purchase #7	$38.38	10.743%	$42.5032	$42.50	$42.50	$42.50
7 purchase totals =	$631.63		$695.7596	$695.75	$695.75	$695.70