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	$6.95	6.333%	$7.3901	$7.39	$7.40	$7.40
Purchase #2	$63.74	13.318%	$72.2289	$72.23	$72.25	$72.20
Purchase #3	$51.65	4.866%	$54.1633	$54.16	$54.15	$54.20
Purchase #4	$206.49	7.725%	$222.4414	$222.44	$222.45	$222.40
Purchase #5	$6.98	9.308%	$7.6297	$7.63	$7.65	$7.60
Purchase #6	$40.49	3.314%	$41.8318	$41.83	$41.85	$41.80
Purchase #7	$164.47	9.488%	$180.0749	$180.07	$180.05	$180.10
7 purchase totals =	$540.77		$585.7601	$585.75	$585.80	$585.70