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 $221.38   6.260%   $235.2384   $235.24   $235.25   $235.20  
  Purchase #2 $135.87   9.419%   $148.6676   $148.67   $148.65   $148.70  
  Purchase #3 $179.35   5.174%   $188.6296   $188.63   $188.65   $188.60  
  Purchase #4 $144.28   13.595%   $163.8949   $163.89   $163.90   $163.90  
  Purchase #5 $237.35   12.398%   $266.7767   $266.78   $266.80   $266.80  
  Purchase #6 $218.63   11.270%   $243.2696   $243.27   $243.25   $243.30  
  Purchase #7 $15.47   6.115%   $16.416   $16.42   $16.40   $16.40  
  7 purchase totals = $1,152.33       $1,262.8928   $1,262.90   $1,262.90   $1,262.90