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 $68.95   9.641%   $75.5975   $75.60   $75.60   $75.60  
  Purchase #2 $152.86   11.750%   $170.8211   $170.82   $170.80   $170.80  
  Purchase #3 $59.73   13.149%   $67.5839   $67.58   $67.60   $67.60  
  Purchase #4 $208.31   8.578%   $226.1788   $226.18   $226.20   $226.20  
  Purchase #5 $143.73   13.357%   $162.928   $162.93   $162.95   $162.90  
  Purchase #6 $207.40   13.861%   $236.1477   $236.15   $236.15   $236.10  
  Purchase #7 $55.92   5.763%   $59.1427   $59.14   $59.15   $59.10  
  7 purchase totals = $896.90       $998.3997   $998.40   $998.45   $998.30