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	$33.31	6.181%	$35.3689	$35.37	$35.35	$35.40
Purchase #2	$67.81	9.385%	$74.174	$74.17	$74.15	$74.20
Purchase #3	$143.77	8.533%	$156.0379	$156.04	$156.05	$156.00
Purchase #4	$77.90	6.554%	$83.0056	$83.01	$83.00	$83.00
Purchase #5	$69.38	11.865%	$77.6119	$77.61	$77.60	$77.60
Purchase #6	$72.70	7.709%	$78.3044	$78.30	$78.30	$78.30
Purchase #7	$104.59	6.614%	$111.5076	$111.51	$111.50	$111.50
7 purchase totals =	$569.46		$616.0103	$616.01	$615.95	$616.00