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	$6.84	8.521%	$7.4228	$7.42	$7.40	$7.40
Purchase #2	$158.64	8.669%	$172.3925	$172.39	$172.40	$172.40
Purchase #3	$136.54	12.463%	$153.557	$153.56	$153.55	$153.60
Purchase #4	$92.64	6.408%	$98.5764	$98.58	$98.60	$98.60
Purchase #5	$168.80	3.610%	$174.8937	$174.89	$174.90	$174.90
Purchase #6	$83.67	13.465%	$94.9362	$94.94	$94.95	$94.90
Purchase #7	$143.26	6.262%	$152.2309	$152.23	$152.25	$152.20
7 purchase totals =	$790.39		$854.0095	$854.01	$854.05	$854.00