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 $134.57   5.723%   $142.2714   $142.27   $142.25   $142.30  
  Purchase #2 $11.94   8.524%   $12.9578   $12.96   $12.95   $13.00  
  Purchase #3 $221.88   8.584%   $240.9262   $240.93   $240.95   $240.90  
  Purchase #4 $151.59   11.622%   $169.2078   $169.21   $169.20   $169.20  
  Purchase #5 $74.53   10.867%   $82.6292   $82.63   $82.65   $82.60  
  Purchase #6 $229.38   10.126%   $252.607   $252.61   $252.60   $252.60  
  Purchase #7 $112.75   9.686%   $123.671   $123.67   $123.65   $123.70  
  7 purchase totals = $936.64       $1,024.2704   $1,024.28   $1,024.25   $1,024.30