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	$157.57	12.224%	$176.8314	$176.83	$176.85	$176.80
Purchase #2	$150.34	9.410%	$164.487	$164.49	$164.50	$164.50
Purchase #3	$27.54	13.135%	$31.1574	$31.16	$31.15	$31.20
Purchase #4	$69.91	6.527%	$74.473	$74.47	$74.45	$74.50
Purchase #5	$211.25	10.635%	$233.7164	$233.72	$233.70	$233.70
Purchase #6	$43.37	5.708%	$45.8456	$45.85	$45.85	$45.80
Purchase #7	$6.95	6.828%	$7.4245	$7.42	$7.40	$7.40
7 purchase totals =	$666.93		$733.9353	$733.94	$733.90	$733.90