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	$128.38	7.239%	$137.6734	$137.67	$137.65	$137.70
Purchase #2	$37.46	13.232%	$42.4167	$42.42	$42.40	$42.40
Purchase #3	$89.48	12.705%	$100.8484	$100.85	$100.85	$100.80
Purchase #4	$157.48	7.841%	$169.828	$169.83	$169.85	$169.80
Purchase #5	$193.34	8.307%	$209.4008	$209.40	$209.40	$209.40
Purchase #6	$124.74	6.481%	$132.8244	$132.82	$132.80	$132.80
Purchase #7	$31.25	13.287%	$35.4022	$35.40	$35.40	$35.40
7 purchase totals =	$762.13		$828.3939	$828.39	$828.35	$828.30