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	$32.94	13.675%	$37.4445	$37.44	$37.45	$37.40
Purchase #2	$112.38	7.180%	$120.4489	$120.45	$120.45	$120.40
Purchase #3	$25.88	10.792%	$28.673	$28.67	$28.65	$28.70
Purchase #4	$33.39	5.120%	$35.0996	$35.10	$35.10	$35.10
Purchase #5	$93.50	11.161%	$103.9355	$103.94	$103.95	$103.90
Purchase #6	$11.40	6.211%	$12.1081	$12.11	$12.10	$12.10
Purchase #7	$80.43	11.536%	$89.7084	$89.71	$89.70	$89.70
7 purchase totals =	$389.92		$427.4180	$427.42	$427.40	$427.30