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 $248.44   7.589%   $267.2941   $267.29   $267.30   $267.30  
  Purchase #2 $223.46   6.461%   $237.8978   $237.90   $237.90   $237.90  
  Purchase #3 $151.37   9.216%   $165.3203   $165.32   $165.30   $165.30  
  Purchase #4 $68.83   4.331%   $71.811   $71.81   $71.80   $71.80  
  Purchase #5 $217.30   10.520%   $240.16   $240.16   $240.15   $240.20  
  Purchase #6 $218.45   8.377%   $236.7496   $236.75   $236.75   $236.70  
  Purchase #7 $35.25   7.854%   $38.0185   $38.02   $38.00   $38.00  
  7 purchase totals = $1,163.10       $1,257.2513   $1,257.25   $1,257.20   $1,257.20