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	$86.86	3.510%	$89.9088	$89.91	$89.90	$89.90
Purchase #2	$160.85	4.548%	$168.1655	$168.17	$168.15	$168.20
Purchase #3	$185.31	6.475%	$197.3088	$197.31	$197.30	$197.30
Purchase #4	$108.56	8.493%	$117.78	$117.78	$117.80	$117.80
Purchase #5	$172.77	11.626%	$192.8562	$192.86	$192.85	$192.90
Purchase #6	$170.79	3.862%	$177.3859	$177.39	$177.40	$177.40
Purchase #7	$72.90	6.220%	$77.4344	$77.43	$77.45	$77.40
7 purchase totals =	$958.04		$1,020.8396	$1,020.85	$1,020.85	$1,020.90