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	$199.52	12.706%	$224.871	$224.87	$224.85	$224.90
Purchase #2	$46.86	10.567%	$51.8117	$51.81	$51.80	$51.80
Purchase #3	$165.58	3.669%	$171.6551	$171.66	$171.65	$171.70
Purchase #4	$50.89	5.275%	$53.5744	$53.57	$53.55	$53.60
Purchase #5	$144.48	9.595%	$158.3429	$158.34	$158.35	$158.30
Purchase #6	$134.81	11.804%	$150.723	$150.72	$150.70	$150.70
Purchase #7	$42.90	8.390%	$46.4993	$46.50	$46.50	$46.50
7 purchase totals =	$785.04		$857.4774	$857.47	$857.40	$857.50