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	$20.77	3.822%	$21.5638	$21.56	$21.55	$21.60
Purchase #2	$38.96	9.417%	$42.6289	$42.63	$42.65	$42.60
Purchase #3	$87.79	5.328%	$92.4675	$92.47	$92.45	$92.50
Purchase #4	$37.79	10.715%	$41.8392	$41.84	$41.85	$41.80
Purchase #5	$169.42	12.502%	$190.6009	$190.60	$190.60	$190.60
Purchase #6	$157.42	6.785%	$168.1009	$168.10	$168.10	$168.10
Purchase #7	$234.46	7.833%	$252.8253	$252.83	$252.85	$252.80
7 purchase totals =	$746.61		$810.0265	$810.03	$810.05	$810.00