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	$233.83	4.116%	$243.4544	$243.45	$243.45	$243.50
Purchase #2	$34.30	6.691%	$36.595	$36.60	$36.60	$36.60
Purchase #3	$36.53	3.219%	$37.7059	$37.71	$37.70	$37.70
Purchase #4	$40.99	11.251%	$45.6018	$45.60	$45.60	$45.60
Purchase #5	$216.42	10.335%	$238.787	$238.79	$238.80	$238.80
Purchase #6	$26.89	7.498%	$28.9062	$28.91	$28.90	$28.90
Purchase #7	$10.49	3.217%	$10.8275	$10.83	$10.85	$10.80
7 purchase totals =	$599.45		$641.8778	$641.89	$641.90	$641.90