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	$125.81	13.510%	$142.8069	$142.81	$142.80	$142.80
Purchase #2	$241.28	13.492%	$273.8335	$273.83	$273.85	$273.80
Purchase #3	$58.63	12.179%	$65.7705	$65.77	$65.75	$65.80
Purchase #4	$52.43	13.698%	$59.6119	$59.61	$59.60	$59.60
Purchase #5	$112.98	12.749%	$127.3838	$127.38	$127.40	$127.40
Purchase #6	$54.28	10.348%	$59.8969	$59.90	$59.90	$59.90
Purchase #7	$99.43	13.489%	$112.8421	$112.84	$112.85	$112.80
7 purchase totals =	$744.84		$842.1456	$842.14	$842.15	$842.10