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	$175.65	9.817%	$192.8936	$192.89	$192.90	$192.90
Purchase #2	$89.77	12.402%	$100.9033	$100.90	$100.90	$100.90
Purchase #3	$45.56	5.517%	$48.0735	$48.07	$48.05	$48.10
Purchase #4	$144.76	8.309%	$156.7881	$156.79	$156.80	$156.80
Purchase #5	$116.57	3.355%	$120.4809	$120.48	$120.50	$120.50
Purchase #6	$170.89	6.391%	$181.8116	$181.81	$181.80	$181.80
Purchase #7	$91.82	4.223%	$95.6976	$95.70	$95.70	$95.70
7 purchase totals =	$835.02		$896.6486	$896.64	$896.65	$896.70