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	$78.96	4.204%	$82.2795	$82.28	$82.30	$82.30
Purchase #2	$90.33	8.595%	$98.0939	$98.09	$98.10	$98.10
Purchase #3	$136.51	3.515%	$141.3083	$141.31	$141.30	$141.30
Purchase #4	$35.70	4.605%	$37.344	$37.34	$37.35	$37.30
Purchase #5	$234.97	4.699%	$246.0112	$246.01	$246.00	$246.00
Purchase #6	$34.33	9.725%	$37.6686	$37.67	$37.65	$37.70
Purchase #7	$35.76	10.800%	$39.6221	$39.62	$39.60	$39.60
7 purchase totals =	$646.56		$682.3276	$682.32	$682.30	$682.30