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	$112.85	7.326%	$121.1174	$121.12	$121.10	$121.10
Purchase #2	$44.41	8.375%	$48.1293	$48.13	$48.15	$48.10
Purchase #3	$107.66	6.441%	$114.5944	$114.59	$114.60	$114.60
Purchase #4	$56.77	4.792%	$59.4904	$59.49	$59.50	$59.50
Purchase #5	$49.44	11.319%	$55.0361	$55.04	$55.05	$55.00
Purchase #6	$160.82	9.164%	$175.5575	$175.56	$175.55	$175.60
Purchase #7	$90.67	3.540%	$93.8797	$93.88	$93.90	$93.90
7 purchase totals =	$622.62		$667.8048	$667.81	$667.85	$667.80