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	$191.84	3.431%	$198.422	$198.42	$198.40	$198.40
Purchase #2	$129.99	10.785%	$144.0094	$144.01	$144.00	$144.00
Purchase #3	$78.81	13.489%	$89.4407	$89.44	$89.45	$89.40
Purchase #4	$113.79	11.150%	$126.4776	$126.48	$126.50	$126.50
Purchase #5	$185.49	7.514%	$199.4277	$199.43	$199.45	$199.40
Purchase #6	$11.88	13.719%	$13.5098	$13.51	$13.50	$13.50
Purchase #7	$204.62	10.532%	$226.1706	$226.17	$226.15	$226.20
7 purchase totals =	$916.42		$997.4578	$997.46	$997.45	$997.40