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	$100.78	3.380%	$104.1864	$104.19	$104.20	$104.20
Purchase #2	$247.30	12.522%	$278.2669	$278.27	$278.25	$278.30
Purchase #3	$115.45	8.414%	$125.164	$125.16	$125.15	$125.20
Purchase #4	$136.34	6.167%	$144.7481	$144.75	$144.75	$144.70
Purchase #5	$7.52	4.556%	$7.8626	$7.86	$7.85	$7.90
Purchase #6	$214.81	10.871%	$238.162	$238.16	$238.15	$238.20
Purchase #7	$95.27	4.453%	$99.5124	$99.51	$99.50	$99.50
7 purchase totals =	$917.47		$997.9024	$997.90	$997.85	$998.00