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	$35.82	13.641%	$40.7062	$40.71	$40.70	$40.70
Purchase #2	$207.95	10.826%	$230.4627	$230.46	$230.45	$230.50
Purchase #3	$64.51	9.681%	$70.7552	$70.76	$70.75	$70.80
Purchase #4	$13.90	6.123%	$14.7511	$14.75	$14.75	$14.80
Purchase #5	$54.44	8.697%	$59.1746	$59.17	$59.15	$59.20
Purchase #6	$169.38	3.467%	$175.2524	$175.25	$175.25	$175.30
Purchase #7	$80.59	9.461%	$88.2146	$88.21	$88.20	$88.20
7 purchase totals =	$626.59		$679.3168	$679.31	$679.25	$679.50