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	$117.98	12.151%	$132.3157	$132.32	$132.30	$132.30
Purchase #2	$178.25	6.778%	$190.3318	$190.33	$190.35	$190.30
Purchase #3	$52.54	12.460%	$59.0865	$59.09	$59.10	$59.10
Purchase #4	$147.36	6.801%	$157.382	$157.38	$157.40	$157.40
Purchase #5	$121.47	3.193%	$125.3485	$125.35	$125.35	$125.30
Purchase #6	$96.47	13.676%	$109.6632	$109.66	$109.65	$109.70
Purchase #7	$45.29	6.699%	$48.324	$48.32	$48.30	$48.30
7 purchase totals =	$759.36		$822.4517	$822.45	$822.45	$822.40