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	$48.79	3.213%	$50.3576	$50.36	$50.35	$50.40
Purchase #2	$102.28	6.505%	$108.9333	$108.93	$108.95	$108.90
Purchase #3	$21.89	13.705%	$24.89	$24.89	$24.90	$24.90
Purchase #4	$156.50	7.278%	$167.8901	$167.89	$167.90	$167.90
Purchase #5	$118.27	9.670%	$129.7067	$129.71	$129.70	$129.70
Purchase #6	$188.55	6.148%	$200.1421	$200.14	$200.15	$200.10
Purchase #7	$122.62	3.646%	$127.0907	$127.09	$127.10	$127.10
7 purchase totals =	$758.90		$809.0105	$809.01	$809.05	$809.00