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	$87.81	13.301%	$99.4896	$99.49	$99.50	$99.50
Purchase #2	$172.79	11.229%	$192.1926	$192.19	$192.20	$192.20
Purchase #3	$131.75	9.250%	$143.9369	$143.94	$143.95	$143.90
Purchase #4	$28.66	10.281%	$31.6065	$31.61	$31.60	$31.60
Purchase #5	$137.47	11.105%	$152.736	$152.74	$152.75	$152.70
Purchase #6	$44.45	11.270%	$49.4595	$49.46	$49.45	$49.50
Purchase #7	$134.75	6.354%	$143.312	$143.31	$143.30	$143.30
7 purchase totals =	$737.68		$812.7331	$812.74	$812.75	$812.70