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	$159.47	3.189%	$164.5555	$164.56	$164.55	$164.60
Purchase #2	$37.49	12.330%	$42.1125	$42.11	$42.10	$42.10
Purchase #3	$92.77	7.808%	$100.0135	$100.01	$100.00	$100.00
Purchase #4	$17.70	12.426%	$19.8994	$19.90	$19.90	$19.90
Purchase #5	$37.56	8.270%	$40.6662	$40.67	$40.65	$40.70
Purchase #6	$53.52	13.132%	$60.5482	$60.55	$60.55	$60.50
Purchase #7	$56.97	10.369%	$62.8772	$62.88	$62.90	$62.90
7 purchase totals =	$455.48		$490.6725	$490.68	$490.65	$490.70