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 $44.47   4.872%   $46.6366   $46.64   $46.65   $46.60  
  Purchase #2 $115.43   8.353%   $125.0719   $125.07   $125.05   $125.10  
  Purchase #3 $61.91   6.285%   $65.801   $65.80   $65.80   $65.80  
  Purchase #4 $215.56   5.873%   $228.2198   $228.22   $228.20   $228.20  
  Purchase #5 $190.72   10.761%   $211.2434   $211.24   $211.25   $211.20  
  Purchase #6 $163.95   11.175%   $182.2714   $182.27   $182.25   $182.30  
  Purchase #7 $132.57   4.759%   $138.879   $138.88   $138.90   $138.90  
  7 purchase totals = $924.61       $998.1231   $998.12   $998.10   $998.10