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	$129.71	12.539%	$145.9743	$145.97	$145.95	$146.00
Purchase #2	$42.55	9.165%	$46.4497	$46.45	$46.45	$46.40
Purchase #3	$79.91	10.617%	$88.394	$88.39	$88.40	$88.40
Purchase #4	$83.96	7.466%	$90.2285	$90.23	$90.25	$90.20
Purchase #5	$203.77	13.605%	$231.4929	$231.49	$231.50	$231.50
Purchase #6	$49.88	10.330%	$55.0326	$55.03	$55.05	$55.00
Purchase #7	$167.86	11.763%	$187.6054	$187.61	$187.60	$187.60
7 purchase totals =	$757.64		$845.1774	$845.17	$845.20	$845.10