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	$70.49	8.544%	$76.5127	$76.51	$76.50	$76.50
Purchase #2	$134.81	11.578%	$150.4183	$150.42	$150.40	$150.40
Purchase #3	$78.78	12.811%	$88.8725	$88.87	$88.85	$88.90
Purchase #4	$35.78	7.115%	$38.3257	$38.33	$38.35	$38.30
Purchase #5	$142.60	9.732%	$156.4778	$156.48	$156.50	$156.50
Purchase #6	$62.77	3.527%	$64.9839	$64.98	$65.00	$65.00
Purchase #7	$148.66	12.398%	$167.0909	$167.09	$167.10	$167.10
7 purchase totals =	$673.89		$742.6818	$742.68	$742.70	$742.70