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	$59.33	11.185%	$65.9661	$65.97	$65.95	$66.00
Purchase #2	$90.40	10.638%	$100.0168	$100.02	$100.00	$100.00
Purchase #3	$148.25	6.443%	$157.8017	$157.80	$157.80	$157.80
Purchase #4	$182.87	5.756%	$193.396	$193.40	$193.40	$193.40
Purchase #5	$118.95	3.412%	$123.0086	$123.01	$123.00	$123.00
Purchase #6	$179.46	11.715%	$200.4837	$200.48	$200.50	$200.50
Purchase #7	$134.42	10.759%	$148.8822	$148.88	$148.90	$148.90
7 purchase totals =	$913.68		$989.5551	$989.56	$989.55	$989.60