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	$27.48	6.505%	$29.2676	$29.27	$29.25	$29.30
Purchase #2	$37.83	9.807%	$41.54	$41.54	$41.55	$41.50
Purchase #3	$6.70	3.659%	$6.9452	$6.95	$6.95	$6.90
Purchase #4	$66.91	10.372%	$73.8499	$73.85	$73.85	$73.80
Purchase #5	$49.63	12.447%	$55.8074	$55.81	$55.80	$55.80
Purchase #6	$12.83	7.677%	$13.815	$13.82	$13.80	$13.80
Purchase #7	$49.40	6.107%	$52.4169	$52.42	$52.40	$52.40
7 purchase totals =	$250.78		$273.6420	$273.66	$273.60	$273.50