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	$35.64	11.704%	$39.8113	$39.81	$39.80	$39.80
Purchase #2	$230.79	6.414%	$245.5929	$245.59	$245.60	$245.60
Purchase #3	$102.89	6.684%	$109.7672	$109.77	$109.75	$109.80
Purchase #4	$63.31	6.855%	$67.6499	$67.65	$67.65	$67.60
Purchase #5	$34.87	8.675%	$37.895	$37.90	$37.90	$37.90
Purchase #6	$164.26	8.700%	$178.5506	$178.55	$178.55	$178.60
Purchase #7	$89.76	5.175%	$94.4051	$94.41	$94.40	$94.40
7 purchase totals =	$721.52		$773.6720	$773.68	$773.65	$773.70