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 $91.38   4.759%   $95.7288   $95.73   $95.75   $95.70  
  Purchase #2 $234.97   6.558%   $250.3793   $250.38   $250.40   $250.40  
  Purchase #3 $111.63   9.362%   $122.0808   $122.08   $122.10   $122.10  
  Purchase #4 $193.26   8.384%   $209.4629   $209.46   $209.45   $209.50  
  Purchase #5 $27.70   7.273%   $29.7146   $29.71   $29.70   $29.70  
  Purchase #6 $218.85   8.201%   $236.7979   $236.80   $236.80   $236.80  
  Purchase #7 $14.73   6.696%   $15.7163   $15.72   $15.70   $15.70  
  7 purchase totals = $892.52       $959.8806   $959.88   $959.90   $959.90