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	$141.39	13.342%	$160.2543	$160.25	$160.25	$160.30
Purchase #2	$244.82	12.342%	$275.0357	$275.04	$275.05	$275.00
Purchase #3	$110.73	11.319%	$123.2635	$123.26	$123.25	$123.30
Purchase #4	$121.26	13.187%	$137.2506	$137.25	$137.25	$137.30
Purchase #5	$237.44	7.466%	$255.1673	$255.17	$255.15	$255.20
Purchase #6	$134.59	3.586%	$139.4164	$139.42	$139.40	$139.40
Purchase #7	$157.88	5.867%	$167.1428	$167.14	$167.15	$167.10
7 purchase totals =	$1,148.11		$1,257.5306	$1,257.53	$1,257.50	$1,257.60