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	$66.45	6.197%	$70.5679	$70.57	$70.55	$70.60
Purchase #2	$57.72	3.445%	$59.7085	$59.71	$59.70	$59.70
Purchase #3	$224.76	6.313%	$238.9491	$238.95	$238.95	$238.90
Purchase #4	$111.65	5.830%	$118.1592	$118.16	$118.15	$118.20
Purchase #5	$245.58	3.837%	$255.0029	$255.00	$255.00	$255.00
Purchase #6	$153.26	5.664%	$161.9406	$161.94	$161.95	$161.90
Purchase #7	$31.98	11.174%	$35.5534	$35.55	$35.55	$35.60
7 purchase totals =	$891.40		$939.8816	$939.88	$939.85	$939.90