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	$37.66	7.191%	$40.3681	$40.37	$40.35	$40.40
Purchase #2	$197.62	5.400%	$208.2915	$208.29	$208.30	$208.30
Purchase #3	$33.85	4.557%	$35.3925	$35.39	$35.40	$35.40
Purchase #4	$178.73	12.406%	$200.9032	$200.90	$200.90	$200.90
Purchase #5	$83.89	9.441%	$91.8101	$91.81	$91.80	$91.80
Purchase #6	$200.45	11.633%	$223.7683	$223.77	$223.75	$223.80
Purchase #7	$124.97	10.360%	$137.9169	$137.92	$137.90	$137.90
7 purchase totals =	$857.17		$938.4506	$938.45	$938.40	$938.50