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 $54.62   5.242%   $57.4832   $57.48   $57.50   $57.50  
  Purchase #2 $169.63   13.145%   $191.9279   $191.93   $191.95   $191.90  
  Purchase #3 $9.74   12.163%   $10.9247   $10.92   $10.90   $10.90  
  Purchase #4 $150.60   10.564%   $166.5094   $166.51   $166.50   $166.50  
  Purchase #5 $182.97   8.545%   $198.6048   $198.60   $198.60   $198.60  
  Purchase #6 $196.68   13.190%   $222.6221   $222.62   $222.60   $222.60  
  Purchase #7 $26.63   8.671%   $28.9391   $28.94   $28.95   $28.90  
  7 purchase totals = $790.87       $877.0112   $877.00   $877.00   $876.90