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	$214.52	6.653%	$228.792	$228.79	$228.80	$228.80
Purchase #2	$143.74	11.738%	$160.6122	$160.61	$160.60	$160.60
Purchase #3	$229.61	11.701%	$256.4767	$256.48	$256.50	$256.50
Purchase #4	$33.62	6.456%	$35.7905	$35.79	$35.80	$35.80
Purchase #5	$34.38	4.641%	$35.9756	$35.98	$36.00	$36.00
Purchase #6	$137.82	12.660%	$155.268	$155.27	$155.25	$155.30
Purchase #7	$98.96	4.372%	$103.2865	$103.29	$103.30	$103.30
7 purchase totals =	$892.65		$976.2015	$976.21	$976.25	$976.30