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 $241.85   8.198%   $261.6769   $261.68   $261.70   $261.70  
  Purchase #2 $163.67   10.730%   $181.2318   $181.23   $181.25   $181.20  
  Purchase #3 $154.28   10.807%   $170.953   $170.95   $170.95   $171.00  
  Purchase #4 $103.78   6.411%   $110.4333   $110.43   $110.45   $110.40  
  Purchase #5 $107.50   8.738%   $116.8934   $116.89   $116.90   $116.90  
  Purchase #6 $173.38   3.324%   $179.1432   $179.14   $179.15   $179.10  
  Purchase #7 $190.49   11.506%   $212.4078   $212.41   $212.40   $212.40  
  7 purchase totals = $1,134.95       $1,232.7394   $1,232.73   $1,232.80   $1,232.70