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 $57.36   13.376%   $65.0325   $65.03   $65.05   $65.00  
  Purchase #2 $136.38   8.792%   $148.3705   $148.37   $148.35   $148.40  
  Purchase #3 $235.97   10.235%   $260.1215   $260.12   $260.10   $260.10  
  Purchase #4 $179.54   6.521%   $191.2478   $191.25   $191.25   $191.20  
  Purchase #5 $14.55   9.645%   $15.9533   $15.95   $15.95   $16.00  
  Purchase #6 $125.93   9.822%   $138.2988   $138.30   $138.30   $138.30  
  Purchase #7 $85.54   8.465%   $92.781   $92.78   $92.80   $92.80  
  7 purchase totals = $835.27       $911.8054   $911.80   $911.80   $911.80