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	$72.83	13.308%	$82.5222	$82.52	$82.50	$82.50
Purchase #2	$30.94	7.282%	$33.1931	$33.19	$33.20	$33.20
Purchase #3	$135.97	10.434%	$150.1571	$150.16	$150.15	$150.20
Purchase #4	$129.71	12.157%	$145.4788	$145.48	$145.50	$145.50
Purchase #5	$140.85	3.555%	$145.8572	$145.86	$145.85	$145.90
Purchase #6	$230.90	10.653%	$255.4978	$255.50	$255.50	$255.50
Purchase #7	$50.25	5.684%	$53.1062	$53.11	$53.10	$53.10
7 purchase totals =	$791.45		$865.8124	$865.82	$865.80	$865.90