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	$38.29	4.264%	$39.9227	$39.92	$39.90	$39.90
Purchase #2	$145.40	11.833%	$162.6052	$162.61	$162.60	$162.60
Purchase #3	$55.86	9.801%	$61.3348	$61.33	$61.35	$61.30
Purchase #4	$134.41	3.769%	$139.4759	$139.48	$139.50	$139.50
Purchase #5	$169.83	10.221%	$187.1883	$187.19	$187.20	$187.20
Purchase #6	$211.93	5.248%	$223.0521	$223.05	$223.05	$223.10
Purchase #7	$123.41	11.675%	$137.8181	$137.82	$137.80	$137.80
7 purchase totals =	$879.13		$951.3971	$951.40	$951.40	$951.40