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	$134.47	3.394%	$139.0339	$139.03	$139.05	$139.00
Purchase #2	$129.90	5.352%	$136.8522	$136.85	$136.85	$136.90
Purchase #3	$188.76	9.389%	$206.4827	$206.48	$206.50	$206.50
Purchase #4	$74.33	12.175%	$83.3797	$83.38	$83.40	$83.40
Purchase #5	$102.38	4.430%	$106.9154	$106.92	$106.90	$106.90
Purchase #6	$236.30	10.335%	$260.7216	$260.72	$260.70	$260.70
Purchase #7	$139.43	5.384%	$146.9369	$146.94	$146.95	$146.90
7 purchase totals =	$1,005.57		$1,080.3224	$1,080.32	$1,080.35	$1,080.30