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	$7.26	8.245%	$7.8586	$7.86	$7.85	$7.90
Purchase #2	$222.99	9.664%	$244.5398	$244.54	$244.55	$244.50
Purchase #3	$78.46	5.669%	$82.9079	$82.91	$82.90	$82.90
Purchase #4	$250.57	6.625%	$267.1703	$267.17	$267.15	$267.20
Purchase #5	$32.36	8.551%	$35.1271	$35.13	$35.15	$35.10
Purchase #6	$33.75	3.373%	$34.8884	$34.89	$34.90	$34.90
Purchase #7	$173.45	10.378%	$191.4506	$191.45	$191.45	$191.50
7 purchase totals =	$798.84		$863.9427	$863.95	$863.95	$864.00