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 $212.60   8.660%   $231.0112   $231.01   $231.00   $231.00  
  Purchase #2 $61.94   12.528%   $69.6998   $69.70   $69.70   $69.70  
  Purchase #3 $133.72   3.259%   $138.0779   $138.08   $138.10   $138.10  
  Purchase #4 $45.95   12.863%   $51.8605   $51.86   $51.85   $51.90  
  Purchase #5 $195.26   9.280%   $213.3801   $213.38   $213.40   $213.40  
  Purchase #6 $93.75   4.630%   $98.0906   $98.09   $98.10   $98.10  
  Purchase #7 $136.38   8.623%   $148.14   $148.14   $148.15   $148.10  
  7 purchase totals = $879.60       $950.2601   $950.26   $950.30   $950.30