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	$28.78	9.640%	$31.5544	$31.55	$31.55	$31.60
Purchase #2	$47.44	8.156%	$51.3092	$51.31	$51.30	$51.30
Purchase #3	$72.49	12.575%	$81.6056	$81.61	$81.60	$81.60
Purchase #4	$53.64	11.195%	$59.645	$59.65	$59.65	$59.60
Purchase #5	$113.29	8.706%	$123.153	$123.15	$123.15	$123.20
Purchase #6	$49.38	9.110%	$53.8785	$53.88	$53.90	$53.90
Purchase #7	$188.42	10.645%	$208.4773	$208.48	$208.50	$208.50
7 purchase totals =	$553.44		$609.6230	$609.63	$609.65	$609.70