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	$241.79	10.285%	$266.6581	$266.66	$266.65	$266.70
Purchase #2	$55.48	10.110%	$61.089	$61.09	$61.10	$61.10
Purchase #3	$96.81	3.859%	$100.5459	$100.55	$100.55	$100.50
Purchase #4	$68.56	13.259%	$77.6504	$77.65	$77.65	$77.70
Purchase #5	$113.61	9.388%	$124.2757	$124.28	$124.30	$124.30
Purchase #6	$83.64	13.594%	$95.01	$95.01	$95.00	$95.00
Purchase #7	$88.70	3.631%	$91.9207	$91.92	$91.90	$91.90
7 purchase totals =	$748.59		$817.1498	$817.16	$817.15	$817.20