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 $126.66   9.128%   $138.2215   $138.22   $138.20   $138.20  
  Purchase #2 $201.30   4.249%   $209.8532   $209.85   $209.85   $209.90  
  Purchase #3 $47.38   13.566%   $53.8076   $53.81   $53.80   $53.80  
  Purchase #4 $168.73   11.143%   $187.5316   $187.53   $187.55   $187.50  
  Purchase #5 $118.64   12.634%   $133.629   $133.63   $133.65   $133.60  
  Purchase #6 $55.28   5.611%   $58.3818   $58.38   $58.40   $58.40  
  Purchase #7 $250.86   4.467%   $262.0659   $262.07   $262.05   $262.10  
  7 purchase totals = $968.85       $1,043.4906   $1,043.49   $1,043.50   $1,043.50