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	$132.27	5.218%	$139.1718	$139.17	$139.15	$139.20
Purchase #2	$109.90	8.257%	$118.9744	$118.97	$118.95	$119.00
Purchase #3	$199.56	11.689%	$222.8866	$222.89	$222.90	$222.90
Purchase #4	$220.70	12.364%	$247.9873	$247.99	$248.00	$248.00
Purchase #5	$32.44	10.418%	$35.8196	$35.82	$35.80	$35.80
Purchase #6	$78.43	12.829%	$88.4918	$88.49	$88.50	$88.50
Purchase #7	$28.54	10.240%	$31.4625	$31.46	$31.45	$31.50
7 purchase totals =	$801.84		$884.7940	$884.79	$884.75	$884.90