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	$122.98	6.441%	$130.9011	$130.90	$130.90	$130.90
Purchase #2	$196.66	5.856%	$208.1764	$208.18	$208.20	$208.20
Purchase #3	$42.48	4.264%	$44.2913	$44.29	$44.30	$44.30
Purchase #4	$137.81	13.434%	$156.3234	$156.32	$156.30	$156.30
Purchase #5	$122.35	8.550%	$132.8109	$132.81	$132.80	$132.80
Purchase #6	$151.62	9.341%	$165.7828	$165.78	$165.80	$165.80
Purchase #7	$12.64	7.660%	$13.6082	$13.61	$13.60	$13.60
7 purchase totals =	$786.54		$851.8941	$851.89	$851.90	$851.90