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	$144.89	10.800%	$160.5381	$160.54	$160.55	$160.50
Purchase #2	$36.35	13.264%	$41.1715	$41.17	$41.15	$41.20
Purchase #3	$25.40	10.738%	$28.1275	$28.13	$28.15	$28.10
Purchase #4	$40.85	12.215%	$45.8398	$45.84	$45.85	$45.80
Purchase #5	$199.30	9.636%	$218.5045	$218.50	$218.50	$218.50
Purchase #6	$43.88	3.718%	$45.5115	$45.51	$45.50	$45.50
Purchase #7	$159.63	6.671%	$170.2789	$170.28	$170.30	$170.30
7 purchase totals =	$650.30		$709.9718	$709.97	$710.00	$709.90