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 $59.31   10.750%   $65.6858   $65.69   $65.70   $65.70  
  Purchase #2 $112.95   5.837%   $119.5429   $119.54   $119.55   $119.50  
  Purchase #3 $27.62   11.140%   $30.6969   $30.70   $30.70   $30.70  
  Purchase #4 $235.41   9.235%   $257.1501   $257.15   $257.15   $257.20  
  Purchase #5 $230.34   8.675%   $250.322   $250.32   $250.30   $250.30  
  Purchase #6 $19.67   8.438%   $21.3298   $21.33   $21.35   $21.30  
  Purchase #7 $8.78   6.259%   $9.3295   $9.33   $9.35   $9.30  
  7 purchase totals = $694.08       $754.0570   $754.06   $754.10   $754.00