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	$180.91	9.617%	$198.3081	$198.31	$198.30	$198.30
Purchase #2	$73.94	6.198%	$78.5228	$78.52	$78.50	$78.50
Purchase #3	$195.44	8.715%	$212.4726	$212.47	$212.45	$212.50
Purchase #4	$21.80	12.417%	$24.5069	$24.51	$24.50	$24.50
Purchase #5	$7.77	7.303%	$8.3374	$8.34	$8.35	$8.30
Purchase #6	$154.57	7.125%	$165.5831	$165.58	$165.60	$165.60
Purchase #7	$160.73	7.188%	$172.2833	$172.28	$172.30	$172.30
7 purchase totals =	$795.16		$860.0142	$860.01	$860.00	$860.00