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	$33.70	12.363%	$37.8663	$37.87	$37.85	$37.90
Purchase #2	$50.26	11.277%	$55.9278	$55.93	$55.95	$55.90
Purchase #3	$68.41	4.601%	$71.5575	$71.56	$71.55	$71.60
Purchase #4	$35.89	9.191%	$39.1886	$39.19	$39.20	$39.20
Purchase #5	$74.59	5.524%	$78.7104	$78.71	$78.70	$78.70
Purchase #6	$156.81	4.737%	$164.2381	$164.24	$164.25	$164.20
Purchase #7	$56.70	8.626%	$61.5909	$61.59	$61.60	$61.60
7 purchase totals =	$476.36		$509.0796	$509.09	$509.10	$509.10