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 $51.31   13.588%   $58.282   $58.28   $58.30   $58.30  
  Purchase #2 $158.63   9.625%   $173.8981   $173.90   $173.90   $173.90  
  Purchase #3 $174.86   11.355%   $194.7154   $194.72   $194.70   $194.70  
  Purchase #4 $9.47   6.660%   $10.1007   $10.10   $10.10   $10.10  
  Purchase #5 $138.71   7.126%   $148.5945   $148.59   $148.60   $148.60  
  Purchase #6 $8.83   5.605%   $9.3249   $9.32   $9.30   $9.30  
  Purchase #7 $99.88   13.350%   $113.214   $113.21   $113.20   $113.20  
  7 purchase totals = $641.69       $708.1296   $708.12   $708.10   $708.10