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	$221.30	11.294%	$246.2936	$246.29	$246.30	$246.30
Purchase #2	$74.96	3.813%	$77.8182	$77.82	$77.80	$77.80
Purchase #3	$166.48	10.301%	$183.6291	$183.63	$183.65	$183.60
Purchase #4	$78.57	8.191%	$85.0057	$85.01	$85.00	$85.00
Purchase #5	$85.82	5.407%	$90.4603	$90.46	$90.45	$90.50
Purchase #6	$161.57	5.774%	$170.8991	$170.90	$170.90	$170.90
Purchase #7	$109.54	12.700%	$123.4516	$123.45	$123.45	$123.50
7 purchase totals =	$898.24		$977.5576	$977.56	$977.55	$977.60