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	$49.66	3.661%	$51.4781	$51.48	$51.50	$51.50
Purchase #2	$198.55	13.540%	$225.4337	$225.43	$225.45	$225.40
Purchase #3	$123.53	5.423%	$130.229	$130.23	$130.25	$130.20
Purchase #4	$72.47	8.582%	$78.6894	$78.69	$78.70	$78.70
Purchase #5	$115.83	6.577%	$123.4481	$123.45	$123.45	$123.40
Purchase #6	$225.66	12.459%	$253.775	$253.78	$253.80	$253.80
Purchase #7	$160.60	12.517%	$180.7023	$180.70	$180.70	$180.70
7 purchase totals =	$946.30		$1,043.7556	$1,043.76	$1,043.85	$1,043.70