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	$37.73	11.339%	$42.0082	$42.01	$42.00	$42.00
Purchase #2	$131.49	4.604%	$137.5438	$137.54	$137.55	$137.50
Purchase #3	$103.44	6.359%	$110.0177	$110.02	$110.00	$110.00
Purchase #4	$38.64	13.547%	$43.8746	$43.87	$43.85	$43.90
Purchase #5	$246.50	5.139%	$259.1676	$259.17	$259.15	$259.20
Purchase #6	$84.35	10.123%	$92.8888	$92.89	$92.90	$92.90
Purchase #7	$57.75	10.234%	$63.6601	$63.66	$63.65	$63.70
7 purchase totals =	$699.90		$749.1608	$749.16	$749.10	$749.20