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	$185.56	3.742%	$192.5037	$192.50	$192.50	$192.50
Purchase #2	$131.82	3.719%	$136.7224	$136.72	$136.70	$136.70
Purchase #3	$63.31	12.338%	$71.1212	$71.12	$71.10	$71.10
Purchase #4	$148.34	3.475%	$153.4948	$153.49	$153.50	$153.50
Purchase #5	$146.32	12.492%	$164.5983	$164.60	$164.60	$164.60
Purchase #6	$81.45	6.830%	$87.013	$87.01	$87.00	$87.00
Purchase #7	$68.81	10.482%	$76.0227	$76.02	$76.00	$76.00
7 purchase totals =	$825.61		$881.4761	$881.46	$881.40	$881.40