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	$76.69	6.510%	$81.6825	$81.68	$81.70	$81.70
Purchase #2	$198.91	12.857%	$224.4839	$224.48	$224.50	$224.50
Purchase #3	$42.85	5.379%	$45.1549	$45.15	$45.15	$45.20
Purchase #4	$81.92	9.580%	$89.7679	$89.77	$89.75	$89.80
Purchase #5	$213.43	4.558%	$223.1581	$223.16	$223.15	$223.20
Purchase #6	$33.26	5.401%	$35.0564	$35.06	$35.05	$35.10
Purchase #7	$118.48	11.580%	$132.2	$132.20	$132.20	$132.20
7 purchase totals =	$765.54		$831.5037	$831.50	$831.50	$831.70