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 $241.67   5.146%   $254.1063   $254.11   $254.10   $254.10  
  Purchase #2 $56.31   4.176%   $58.6615   $58.66   $58.65   $58.70  
  Purchase #3 $154.75   5.600%   $163.416   $163.42   $163.40   $163.40  
  Purchase #4 $89.87   6.298%   $95.53   $95.53   $95.55   $95.50  
  Purchase #5 $157.65   4.782%   $165.1888   $165.19   $165.20   $165.20  
  Purchase #6 $239.28   11.275%   $266.2588   $266.26   $266.25   $266.30  
  Purchase #7 $236.97   10.422%   $261.667   $261.67   $261.65   $261.70  
  7 purchase totals = $1,176.50       $1,264.8284   $1,264.84   $1,264.80   $1,264.90