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 $104.98   10.706%   $116.2192   $116.22   $116.20   $116.20  
  Purchase #2 $223.62   10.228%   $246.4919   $246.49   $246.50   $246.50  
  Purchase #3 $133.59   11.513%   $148.9702   $148.97   $148.95   $149.00  
  Purchase #4 $248.89   10.855%   $275.907   $275.91   $275.90   $275.90  
  Purchase #5 $54.27   4.353%   $56.6324   $56.63   $56.65   $56.60  
  Purchase #6 $76.60   4.845%   $80.3113   $80.31   $80.30   $80.30  
  Purchase #7 $217.67   3.272%   $224.7922   $224.79   $224.80   $224.80  
  7 purchase totals = $1,059.62       $1,149.3242   $1,149.32   $1,149.30   $1,149.30