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	$71.40	3.482%	$73.8861	$73.89	$73.90	$73.90
Purchase #2	$230.40	3.608%	$238.7128	$238.71	$238.70	$238.70
Purchase #3	$220.93	5.868%	$233.8942	$233.89	$233.90	$233.90
Purchase #4	$13.66	12.774%	$15.4049	$15.40	$15.40	$15.40
Purchase #5	$194.78	11.262%	$216.7161	$216.72	$216.70	$216.70
Purchase #6	$38.58	9.766%	$42.3477	$42.35	$42.35	$42.30
Purchase #7	$114.82	7.555%	$123.4947	$123.49	$123.50	$123.50
7 purchase totals =	$884.57		$944.4565	$944.45	$944.45	$944.40