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 $244.27   11.235%   $271.7137   $271.71   $271.70   $271.70  
  Purchase #2 $77.87   11.153%   $86.5548   $86.55   $86.55   $86.60  
  Purchase #3 $160.37   4.678%   $167.8721   $167.87   $167.85   $167.90  
  Purchase #4 $97.26   11.583%   $108.5256   $108.53   $108.55   $108.50  
  Purchase #5 $6.92   10.220%   $7.6272   $7.63   $7.65   $7.60  
  Purchase #6 $16.32   6.436%   $17.3704   $17.37   $17.35   $17.40  
  Purchase #7 $110.79   13.160%   $125.37   $125.37   $125.35   $125.40  
  7 purchase totals = $713.80       $785.0338   $785.03   $785.00   $785.10