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	$96.27	3.224%	$99.3737	$99.37	$99.35	$99.40
Purchase #2	$76.67	7.633%	$82.5222	$82.52	$82.50	$82.50
Purchase #3	$33.80	5.143%	$35.5383	$35.54	$35.55	$35.50
Purchase #4	$101.85	3.303%	$105.2141	$105.21	$105.20	$105.20
Purchase #5	$140.56	10.755%	$155.6772	$155.68	$155.70	$155.70
Purchase #6	$148.84	5.285%	$156.7062	$156.71	$156.70	$156.70
Purchase #7	$10.46	4.696%	$10.9512	$10.95	$10.95	$11.00
7 purchase totals =	$608.45		$645.9829	$645.98	$645.95	$646.00