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	$70.26	12.390%	$78.9652	$78.97	$78.95	$79.00
Purchase #2	$171.38	6.142%	$181.9062	$181.91	$181.90	$181.90
Purchase #3	$209.71	8.455%	$227.441	$227.44	$227.45	$227.40
Purchase #4	$93.63	5.534%	$98.8115	$98.81	$98.80	$98.80
Purchase #5	$198.45	12.682%	$223.6174	$223.62	$223.60	$223.60
Purchase #6	$31.38	3.493%	$32.4761	$32.48	$32.50	$32.50
Purchase #7	$21.78	13.330%	$24.6833	$24.68	$24.70	$24.70
7 purchase totals =	$796.59		$867.9007	$867.91	$867.90	$867.90