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 $239.61   11.175%   $266.3864   $266.39   $266.40   $266.40  
  Purchase #2 $9.81   8.609%   $10.6545   $10.65   $10.65   $10.70  
  Purchase #3 $53.83   4.327%   $56.1592   $56.16   $56.15   $56.20  
  Purchase #4 $80.43   5.175%   $84.5923   $84.59   $84.60   $84.60  
  Purchase #5 $191.60   13.798%   $218.037   $218.04   $218.05   $218.00  
  Purchase #6 $148.45   11.675%   $165.7815   $165.78   $165.80   $165.80  
  Purchase #7 $212.83   4.284%   $221.9476   $221.95   $221.95   $221.90  
  7 purchase totals = $936.56       $1,023.5585   $1,023.56   $1,023.60   $1,023.60