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	$54.54	5.154%	$57.351	$57.35	$57.35	$57.40
Purchase #2	$223.73	4.378%	$233.5249	$233.52	$233.50	$233.50
Purchase #3	$80.43	4.237%	$83.8378	$83.84	$83.85	$83.80
Purchase #4	$28.45	11.698%	$31.7781	$31.78	$31.80	$31.80
Purchase #5	$127.79	12.357%	$143.581	$143.58	$143.60	$143.60
Purchase #6	$188.74	10.300%	$208.1802	$208.18	$208.20	$208.20
Purchase #7	$136.91	7.180%	$146.7401	$146.74	$146.75	$146.70
7 purchase totals =	$840.59		$904.9931	$904.99	$905.05	$905.00