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	$238.83	11.429%	$266.1259	$266.13	$266.15	$266.10
Purchase #2	$81.68	4.614%	$85.4487	$85.45	$85.45	$85.40
Purchase #3	$88.54	13.700%	$100.67	$100.67	$100.65	$100.70
Purchase #4	$89.47	10.674%	$99.02	$99.02	$99.00	$99.00
Purchase #5	$93.30	13.266%	$105.6772	$105.68	$105.70	$105.70
Purchase #6	$76.47	9.137%	$83.4571	$83.46	$83.45	$83.50
Purchase #7	$90.66	3.308%	$93.659	$93.66	$93.65	$93.70
7 purchase totals =	$758.95		$834.0579	$834.07	$834.05	$834.10