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	$53.78	5.739%	$56.8664	$56.87	$56.85	$56.90
Purchase #2	$100.42	10.246%	$110.709	$110.71	$110.70	$110.70
Purchase #3	$249.32	12.562%	$280.6396	$280.64	$280.65	$280.60
Purchase #4	$35.31	7.359%	$37.9085	$37.91	$37.90	$37.90
Purchase #5	$16.43	11.655%	$18.3449	$18.34	$18.35	$18.30
Purchase #6	$6.82	11.511%	$7.6051	$7.61	$7.60	$7.60
Purchase #7	$111.44	10.793%	$123.4677	$123.47	$123.45	$123.50
7 purchase totals =	$573.52		$635.5412	$635.55	$635.50	$635.50