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 $232.65   12.180%   $260.9868   $260.99   $261.00   $261.00  
  Purchase #2 $131.49   5.491%   $138.7101   $138.71   $138.70   $138.70  
  Purchase #3 $86.61   11.202%   $96.3121   $96.31   $96.30   $96.30  
  Purchase #4 $95.58   6.411%   $101.7076   $101.71   $101.70   $101.70  
  Purchase #5 $91.29   3.249%   $94.256   $94.26   $94.25   $94.30  
  Purchase #6 $32.51   6.838%   $34.733   $34.73   $34.75   $34.70  
  Purchase #7 $25.89   11.532%   $28.8756   $28.88   $28.90   $28.90  
  7 purchase totals = $696.02       $755.5812   $755.59   $755.60   $755.60