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	$10.31	8.361%	$11.172	$11.17	$11.15	$11.20
Purchase #2	$106.25	7.605%	$114.3303	$114.33	$114.35	$114.30
Purchase #3	$143.47	8.853%	$156.1714	$156.17	$156.15	$156.20
Purchase #4	$86.85	6.578%	$92.563	$92.56	$92.55	$92.60
Purchase #5	$6.48	10.138%	$7.1369	$7.14	$7.15	$7.10
Purchase #6	$137.57	9.851%	$151.122	$151.12	$151.10	$151.10
Purchase #7	$132.39	12.162%	$148.4913	$148.49	$148.50	$148.50
7 purchase totals =	$623.32		$680.9869	$680.98	$680.95	$681.00