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	$50.80	9.604%	$55.6788	$55.68	$55.70	$55.70
Purchase #2	$65.96	10.268%	$72.7328	$72.73	$72.75	$72.70
Purchase #3	$125.83	12.142%	$141.1083	$141.11	$141.10	$141.10
Purchase #4	$210.68	3.340%	$217.7167	$217.72	$217.70	$217.70
Purchase #5	$190.83	4.605%	$199.6177	$199.62	$199.60	$199.60
Purchase #6	$37.83	12.247%	$42.463	$42.46	$42.45	$42.50
Purchase #7	$170.77	12.728%	$192.5056	$192.51	$192.50	$192.50
7 purchase totals =	$852.70		$921.8229	$921.83	$921.80	$921.80