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	$83.86	11.635%	$93.6171	$93.62	$93.60	$93.60
Purchase #2	$31.32	13.562%	$35.5676	$35.57	$35.55	$35.60
Purchase #3	$81.68	9.861%	$89.7345	$89.73	$89.75	$89.70
Purchase #4	$147.57	12.218%	$165.6001	$165.60	$165.60	$165.60
Purchase #5	$163.37	10.188%	$180.0141	$180.01	$180.00	$180.00
Purchase #6	$37.46	7.403%	$40.2332	$40.23	$40.25	$40.20
Purchase #7	$13.47	7.252%	$14.4468	$14.45	$14.45	$14.40
7 purchase totals =	$558.73		$619.2134	$619.21	$619.20	$619.10