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 $228.94   7.589%   $246.3143   $246.31   $246.30   $246.30  
  Purchase #2 $123.73   4.219%   $128.9502   $128.95   $128.95   $129.00  
  Purchase #3 $24.63   5.425%   $25.9662   $25.97   $25.95   $26.00  
  Purchase #4 $79.61   12.195%   $89.3184   $89.32   $89.30   $89.30  
  Purchase #5 $100.49   4.848%   $105.3618   $105.36   $105.35   $105.40  
  Purchase #6 $236.79   5.831%   $250.5972   $250.60   $250.60   $250.60  
  Purchase #7 $249.28   3.255%   $257.3941   $257.39   $257.40   $257.40  
  7 purchase totals = $1,043.47       $1,103.9022   $1,103.90   $1,103.85   $1,104.00