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	$19.87	3.633%	$20.5919	$20.59	$20.60	$20.60
Purchase #2	$72.58	8.274%	$78.5853	$78.59	$78.60	$78.60
Purchase #3	$132.62	7.153%	$142.1063	$142.11	$142.10	$142.10
Purchase #4	$46.87	10.434%	$51.7604	$51.76	$51.75	$51.80
Purchase #5	$200.98	10.153%	$221.3855	$221.39	$221.40	$221.40
Purchase #6	$141.43	11.687%	$157.9589	$157.96	$157.95	$158.00
Purchase #7	$209.90	10.707%	$232.374	$232.37	$232.35	$232.40
7 purchase totals =	$824.25		$904.7623	$904.77	$904.75	$904.90