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 $59.34   10.134%   $65.3535   $65.35   $65.35   $65.40  
  Purchase #2 $219.41   7.298%   $235.4225   $235.42   $235.40   $235.40  
  Purchase #3 $155.53   13.844%   $177.0616   $177.06   $177.05   $177.10  
  Purchase #4 $58.72   3.830%   $60.969   $60.97   $60.95   $61.00  
  Purchase #5 $112.39   4.440%   $117.3801   $117.38   $117.40   $117.40  
  Purchase #6 $136.49   12.673%   $153.7874   $153.79   $153.80   $153.80  
  Purchase #7 $50.36   10.831%   $55.8145   $55.81   $55.80   $55.80  
  7 purchase totals = $792.24       $865.7886   $865.78   $865.75   $865.90