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 $207.83   11.126%   $230.9532   $230.95   $230.95   $231.00  
  Purchase #2 $113.83   3.412%   $117.7139   $117.71   $117.70   $117.70  
  Purchase #3 $104.92   5.222%   $110.3989   $110.40   $110.40   $110.40  
  Purchase #4 $226.71   9.412%   $248.0479   $248.05   $248.05   $248.00  
  Purchase #5 $7.55   12.531%   $8.4961   $8.50   $8.50   $8.50  
  Purchase #6 $133.79   4.561%   $139.8922   $139.89   $139.90   $139.90  
  Purchase #7 $56.81   5.553%   $59.9647   $59.96   $59.95   $60.00  
  7 purchase totals = $851.44       $915.4669   $915.46   $915.45   $915.50