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	$203.93	11.557%	$227.4982	$227.50	$227.50	$227.50
Purchase #2	$127.60	3.754%	$132.3901	$132.39	$132.40	$132.40
Purchase #3	$64.87	4.387%	$67.7158	$67.72	$67.70	$67.70
Purchase #4	$57.52	4.110%	$59.8841	$59.88	$59.90	$59.90
Purchase #5	$85.94	4.653%	$89.9388	$89.94	$89.95	$89.90
Purchase #6	$180.85	5.510%	$190.8148	$190.81	$190.80	$190.80
Purchase #7	$61.30	9.112%	$66.8857	$66.89	$66.90	$66.90
7 purchase totals =	$782.01		$835.1275	$835.13	$835.15	$835.10