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	$54.31	7.172%	$58.2051	$58.21	$58.20	$58.20
Purchase #2	$51.60	8.847%	$56.1651	$56.17	$56.15	$56.20
Purchase #3	$186.56	6.746%	$199.1453	$199.15	$199.15	$199.10
Purchase #4	$131.60	12.788%	$148.429	$148.43	$148.45	$148.40
Purchase #5	$89.67	4.257%	$93.4873	$93.49	$93.50	$93.50
Purchase #6	$192.59	3.851%	$200.0066	$200.01	$200.00	$200.00
Purchase #7	$50.76	8.605%	$55.1279	$55.13	$55.15	$55.10
7 purchase totals =	$757.09		$810.5663	$810.59	$810.60	$810.50