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 $61.37   11.746%   $68.5785   $68.58   $68.60   $68.60  
  Purchase #2 $206.58   9.822%   $226.8703   $226.87   $226.85   $226.90  
  Purchase #3 $231.70   11.222%   $257.7014   $257.70   $257.70   $257.70  
  Purchase #4 $126.53   9.756%   $138.8743   $138.87   $138.85   $138.90  
  Purchase #5 $117.56   13.326%   $133.226   $133.23   $133.25   $133.20  
  Purchase #6 $89.64   8.323%   $97.1007   $97.10   $97.10   $97.10  
  Purchase #7 $73.63   5.260%   $77.5029   $77.50   $77.50   $77.50  
  7 purchase totals = $907.01       $999.8541   $999.85   $999.85   $999.90