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	$245.32	4.161%	$255.5278	$255.53	$255.55	$255.50
Purchase #2	$21.66	9.666%	$23.7537	$23.75	$23.75	$23.80
Purchase #3	$85.75	5.519%	$90.4825	$90.48	$90.50	$90.50
Purchase #4	$69.54	4.603%	$72.7409	$72.74	$72.75	$72.70
Purchase #5	$45.30	12.207%	$50.8298	$50.83	$50.85	$50.80
Purchase #6	$60.91	8.812%	$66.2774	$66.28	$66.30	$66.30
Purchase #7	$160.56	12.135%	$180.044	$180.04	$180.05	$180.00
7 purchase totals =	$689.04		$739.6561	$739.65	$739.75	$739.60