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	$230.91	8.496%	$250.5281	$250.53	$250.55	$250.50
Purchase #2	$38.34	4.371%	$40.0158	$40.02	$40.00	$40.00
Purchase #3	$118.31	5.245%	$124.5154	$124.52	$124.50	$124.50
Purchase #4	$37.46	10.336%	$41.3319	$41.33	$41.35	$41.30
Purchase #5	$92.99	4.489%	$97.1643	$97.16	$97.15	$97.20
Purchase #6	$39.45	11.553%	$44.0077	$44.01	$44.00	$44.00
Purchase #7	$72.87	13.422%	$82.6506	$82.65	$82.65	$82.70
7 purchase totals =	$630.33		$680.2138	$680.22	$680.20	$680.20