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 $62.94   11.790%   $70.3606   $70.36   $70.35   $70.40  
  Purchase #2 $240.29   8.484%   $260.6762   $260.68   $260.70   $260.70  
  Purchase #3 $113.41   10.547%   $125.3714   $125.37   $125.35   $125.40  
  Purchase #4 $54.59   3.189%   $56.3309   $56.33   $56.35   $56.30  
  Purchase #5 $48.41   13.577%   $54.9826   $54.98   $55.00   $55.00  
  Purchase #6 $58.44   6.698%   $62.3543   $62.35   $62.35   $62.40  
  Purchase #7 $29.63   10.688%   $32.7969   $32.80   $32.80   $32.80  
  7 purchase totals = $607.71       $662.8729   $662.87   $662.90   $663.00