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 $247.35   5.801%   $261.6988   $261.70   $261.70   $261.70  
  Purchase #2 $237.55   4.280%   $247.7171   $247.72   $247.70   $247.70  
  Purchase #3 $95.33   7.575%   $102.5512   $102.55   $102.55   $102.60  
  Purchase #4 $8.63   5.838%   $9.1338   $9.13   $9.15   $9.10  
  Purchase #5 $245.64   5.138%   $258.261   $258.26   $258.25   $258.30  
  Purchase #6 $214.79   5.468%   $226.5347   $226.53   $226.55   $226.50  
  Purchase #7 $61.75   6.437%   $65.7248   $65.72   $65.70   $65.70  
  7 purchase totals = $1,111.04       $1,171.6214   $1,171.61   $1,171.60   $1,171.60