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	$70.45	9.142%	$76.8905	$76.89	$76.90	$76.90
Purchase #2	$9.89	10.692%	$10.9474	$10.95	$10.95	$10.90
Purchase #3	$110.88	7.421%	$119.1084	$119.11	$119.10	$119.10
Purchase #4	$103.57	9.473%	$113.3812	$113.38	$113.40	$113.40
Purchase #5	$99.67	11.511%	$111.143	$111.14	$111.15	$111.10
Purchase #6	$19.50	8.716%	$21.1996	$21.20	$21.20	$21.20
Purchase #7	$187.92	4.208%	$195.8277	$195.83	$195.85	$195.80
7 purchase totals =	$601.88		$648.4978	$648.50	$648.55	$648.40