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	$103.73	12.551%	$116.7492	$116.75	$116.75	$116.70
Purchase #2	$113.75	8.851%	$123.818	$123.82	$123.80	$123.80
Purchase #3	$141.97	4.226%	$147.9697	$147.97	$147.95	$148.00
Purchase #4	$153.32	12.724%	$172.8284	$172.83	$172.85	$172.80
Purchase #5	$174.75	9.599%	$191.5243	$191.52	$191.50	$191.50
Purchase #6	$18.67	11.256%	$20.7715	$20.77	$20.75	$20.80
Purchase #7	$33.97	3.537%	$35.1715	$35.17	$35.15	$35.20
7 purchase totals =	$740.16		$808.8326	$808.83	$808.75	$808.80