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	$72.25	9.785%	$79.3197	$79.32	$79.30	$79.30
Purchase #2	$243.78	7.578%	$262.2536	$262.25	$262.25	$262.30
Purchase #3	$132.98	9.315%	$145.3671	$145.37	$145.35	$145.40
Purchase #4	$169.30	8.861%	$184.3017	$184.30	$184.30	$184.30
Purchase #5	$14.78	9.808%	$16.2296	$16.23	$16.25	$16.20
Purchase #6	$10.54	12.768%	$11.8857	$11.89	$11.90	$11.90
Purchase #7	$132.62	13.515%	$150.5436	$150.54	$150.55	$150.50
7 purchase totals =	$776.25		$849.9010	$849.90	$849.90	$849.90