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 $133.75   11.402%   $149.0002   $149.00   $149.00   $149.00  
  Purchase #2 $39.93   8.661%   $43.3883   $43.39   $43.40   $43.40  
  Purchase #3 $246.61   5.149%   $259.3079   $259.31   $259.30   $259.30  
  Purchase #4 $31.28   8.701%   $34.0017   $34.00   $34.00   $34.00  
  Purchase #5 $119.99   4.439%   $125.3164   $125.32   $125.30   $125.30  
  Purchase #6 $133.43   13.571%   $151.5378   $151.54   $151.55   $151.50  
  Purchase #7 $247.40   5.631%   $261.3311   $261.33   $261.35   $261.30  
  7 purchase totals = $952.39       $1,023.8834   $1,023.89   $1,023.90   $1,023.80