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 $242.99   5.758%   $256.9814   $256.98   $257.00   $257.00  
  Purchase #2 $218.95   4.591%   $229.002   $229.00   $229.00   $229.00  
  Purchase #3 $107.28   5.659%   $113.351   $113.35   $113.35   $113.40  
  Purchase #4 $193.79   11.647%   $216.3607   $216.36   $216.35   $216.40  
  Purchase #5 $61.83   12.827%   $69.7609   $69.76   $69.75   $69.80  
  Purchase #6 $20.40   10.844%   $22.6122   $22.61   $22.60   $22.60  
  Purchase #7 $179.93   7.675%   $193.7396   $193.74   $193.75   $193.70  
  7 purchase totals = $1,025.17       $1,101.8078   $1,101.80   $1,101.80   $1,101.90