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   7.219%   $265.2062   $265.21   $265.20   $265.20  
  Purchase #2 $211.89   5.838%   $224.2601   $224.26   $224.25   $224.30  
  Purchase #3 $117.70   4.641%   $123.1625   $123.16   $123.15   $123.20  
  Purchase #4 $94.77   7.207%   $101.6001   $101.60   $101.60   $101.60  
  Purchase #5 $167.37   9.825%   $183.8141   $183.81   $183.80   $183.80  
  Purchase #6 $223.68   8.660%   $243.0507   $243.05   $243.05   $243.10  
  Purchase #7 $250.26   4.327%   $261.0888   $261.09   $261.10   $261.10  
  7 purchase totals = $1,313.02       $1,402.1825   $1,402.18   $1,402.15   $1,402.30