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 $236.51   10.426%   $261.1685   $261.17   $261.15   $261.20  
  Purchase #2 $71.75   6.656%   $76.5257   $76.53   $76.55   $76.50  
  Purchase #3 $29.25   11.782%   $32.6962   $32.70   $32.70   $32.70  
  Purchase #4 $83.43   3.506%   $86.3551   $86.36   $86.35   $86.40  
  Purchase #5 $165.61   7.212%   $177.5538   $177.55   $177.55   $177.60  
  Purchase #6 $137.37   12.134%   $154.0385   $154.04   $154.05   $154.00  
  Purchase #7 $247.31   7.750%   $266.4765   $266.48   $266.50   $266.50  
  7 purchase totals = $971.23       $1,054.8143   $1,054.83   $1,054.85   $1,054.90