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	$79.59	7.406%	$85.4844	$85.48	$85.50	$85.50
Purchase #2	$37.68	12.539%	$42.4047	$42.40	$42.40	$42.40
Purchase #3	$20.59	6.760%	$21.9819	$21.98	$22.00	$22.00
Purchase #4	$246.79	3.363%	$255.0895	$255.09	$255.10	$255.10
Purchase #5	$226.96	10.173%	$250.0486	$250.05	$250.05	$250.00
Purchase #6	$173.31	11.153%	$192.6393	$192.64	$192.65	$192.60
Purchase #7	$57.95	10.754%	$64.1819	$64.18	$64.20	$64.20
7 purchase totals =	$842.87		$911.8303	$911.82	$911.90	$911.80