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	$232.84	12.272%	$261.4141	$261.41	$261.40	$261.40
Purchase #2	$68.57	5.535%	$72.3653	$72.37	$72.35	$72.40
Purchase #3	$145.86	5.295%	$153.5833	$153.58	$153.60	$153.60
Purchase #4	$241.47	7.586%	$259.7879	$259.79	$259.80	$259.80
Purchase #5	$183.81	3.665%	$190.5466	$190.55	$190.55	$190.50
Purchase #6	$94.26	10.133%	$103.8114	$103.81	$103.80	$103.80
Purchase #7	$83.32	3.192%	$85.9796	$85.98	$86.00	$86.00
7 purchase totals =	$1,050.13		$1,127.4882	$1,127.49	$1,127.50	$1,127.50