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	$120.91	8.692%	$131.4195	$131.42	$131.40	$131.40
Purchase #2	$31.86	9.193%	$34.7889	$34.79	$34.80	$34.80
Purchase #3	$141.77	3.232%	$146.352	$146.35	$146.35	$146.40
Purchase #4	$119.97	6.285%	$127.5101	$127.51	$127.50	$127.50
Purchase #5	$101.96	6.723%	$108.8148	$108.81	$108.80	$108.80
Purchase #6	$49.67	6.338%	$52.8181	$52.82	$52.80	$52.80
Purchase #7	$140.28	3.257%	$144.8489	$144.85	$144.85	$144.80
7 purchase totals =	$706.42		$746.5523	$746.55	$746.50	$746.50