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	$233.45	11.519%	$260.3411	$260.34	$260.35	$260.30
Purchase #2	$97.74	3.139%	$100.8081	$100.81	$100.80	$100.80
Purchase #3	$53.28	6.694%	$56.8466	$56.85	$56.85	$56.80
Purchase #4	$38.70	3.811%	$40.1749	$40.17	$40.15	$40.20
Purchase #5	$131.37	3.782%	$136.3384	$136.34	$136.35	$136.30
Purchase #6	$34.63	11.198%	$38.5079	$38.51	$38.50	$38.50
Purchase #7	$19.56	13.158%	$22.1337	$22.13	$22.15	$22.10
7 purchase totals =	$608.73		$655.1507	$655.15	$655.15	$655.00