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	$35.37	8.272%	$38.2958	$38.30	$38.30	$38.30
Purchase #2	$175.50	8.549%	$190.5035	$190.50	$190.50	$190.50
Purchase #3	$154.89	8.507%	$168.0665	$168.07	$168.05	$168.10
Purchase #4	$11.58	4.691%	$12.1232	$12.12	$12.10	$12.10
Purchase #5	$83.67	6.587%	$89.1813	$89.18	$89.20	$89.20
Purchase #6	$237.57	11.297%	$264.4083	$264.41	$264.40	$264.40
Purchase #7	$107.49	8.358%	$116.474	$116.47	$116.45	$116.50
7 purchase totals =	$806.07		$879.0526	$879.05	$879.00	$879.10