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	$39.96	7.379%	$42.9086	$42.91	$42.90	$42.90
Purchase #2	$100.72	7.387%	$108.1602	$108.16	$108.15	$108.20
Purchase #3	$152.30	13.418%	$172.7356	$172.74	$172.75	$172.70
Purchase #4	$12.31	9.377%	$13.4643	$13.46	$13.45	$13.50
Purchase #5	$136.70	7.492%	$146.9416	$146.94	$146.95	$146.90
Purchase #6	$216.87	6.515%	$230.9991	$231.00	$231.00	$231.00
Purchase #7	$72.53	11.820%	$81.103	$81.10	$81.10	$81.10
7 purchase totals =	$731.39		$796.3124	$796.31	$796.30	$796.30