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 $248.46   8.243%   $268.9406   $268.94   $268.95   $268.90  
  Purchase #2 $218.51   9.353%   $238.9472   $238.95   $238.95   $238.90  
  Purchase #3 $193.73   8.120%   $209.4609   $209.46   $209.45   $209.50  
  Purchase #4 $25.58   8.490%   $27.7517   $27.75   $27.75   $27.80  
  Purchase #5 $222.27   5.461%   $234.4082   $234.41   $234.40   $234.40  
  Purchase #6 $155.46   13.168%   $175.931   $175.93   $175.95   $175.90  
  Purchase #7 $102.86   12.229%   $115.4387   $115.44   $115.45   $115.40  
  7 purchase totals = $1,166.87       $1,270.8783   $1,270.88   $1,270.90   $1,270.80