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	$121.77	12.727%	$137.2677	$137.27	$137.25	$137.30
Purchase #2	$171.40	9.701%	$188.0275	$188.03	$188.05	$188.00
Purchase #3	$31.30	12.339%	$35.1621	$35.16	$35.15	$35.20
Purchase #4	$164.39	12.285%	$184.5853	$184.59	$184.60	$184.60
Purchase #5	$31.28	3.184%	$32.276	$32.28	$32.30	$32.30
Purchase #6	$179.67	11.274%	$199.926	$199.93	$199.95	$199.90
Purchase #7	$100.87	13.836%	$114.8264	$114.83	$114.85	$114.80
7 purchase totals =	$800.68		$892.0710	$892.09	$892.15	$892.10