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 $190.96   6.826%   $203.9949   $203.99   $204.00   $204.00  
  Purchase #2 $87.90   8.479%   $95.353   $95.35   $95.35   $95.40  
  Purchase #3 $29.55   3.864%   $30.6918   $30.69   $30.70   $30.70  
  Purchase #4 $60.83   9.124%   $66.3801   $66.38   $66.40   $66.40  
  Purchase #5 $61.99   4.811%   $64.9723   $64.97   $64.95   $65.00  
  Purchase #6 $200.59   5.715%   $212.0537   $212.05   $212.05   $212.10  
  Purchase #7 $218.81   13.193%   $247.6776   $247.68   $247.70   $247.70  
  7 purchase totals = $850.63       $921.1234   $921.11   $921.15   $921.30