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	$33.81	11.564%	$37.7198	$37.72	$37.70	$37.70
Purchase #2	$187.59	11.285%	$208.7595	$208.76	$208.75	$208.80
Purchase #3	$92.97	13.778%	$105.7794	$105.78	$105.80	$105.80
Purchase #4	$176.88	7.274%	$189.7463	$189.75	$189.75	$189.70
Purchase #5	$220.80	11.361%	$245.8851	$245.89	$245.90	$245.90
Purchase #6	$135.88	11.699%	$151.7766	$151.78	$151.80	$151.80
Purchase #7	$48.31	8.643%	$52.4854	$52.49	$52.50	$52.50
7 purchase totals =	$896.24		$992.1521	$992.17	$992.20	$992.20