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	$70.76	9.460%	$77.4539	$77.45	$77.45	$77.50
Purchase #2	$238.89	13.766%	$271.7756	$271.78	$271.80	$271.80
Purchase #3	$241.79	13.107%	$273.4814	$273.48	$273.50	$273.50
Purchase #4	$50.61	9.245%	$55.2889	$55.29	$55.30	$55.30
Purchase #5	$37.95	6.862%	$40.5541	$40.55	$40.55	$40.60
Purchase #6	$130.89	12.755%	$147.585	$147.59	$147.60	$147.60
Purchase #7	$23.91	7.761%	$25.7657	$25.77	$25.75	$25.80
7 purchase totals =	$794.80		$891.9046	$891.91	$891.95	$892.10