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	$233.26	3.236%	$240.8083	$240.81	$240.80	$240.80
Purchase #2	$150.31	8.342%	$162.8489	$162.85	$162.85	$162.80
Purchase #3	$82.72	10.706%	$91.576	$91.58	$91.60	$91.60
Purchase #4	$34.33	13.325%	$38.9045	$38.90	$38.90	$38.90
Purchase #5	$64.30	12.226%	$72.1613	$72.16	$72.15	$72.20
Purchase #6	$59.65	5.223%	$62.7655	$62.77	$62.75	$62.80
Purchase #7	$121.91	8.137%	$131.8298	$131.83	$131.85	$131.80
7 purchase totals =	$746.48		$800.8943	$800.90	$800.90	$800.90