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 $141.48   5.526%   $149.2982   $149.30   $149.30   $149.30  
  Purchase #2 $247.43   13.147%   $279.9596   $279.96   $279.95   $280.00  
  Purchase #3 $231.82   8.546%   $251.6313   $251.63   $251.65   $251.60  
  Purchase #4 $85.57   8.545%   $92.882   $92.88   $92.90   $92.90  
  Purchase #5 $163.67   13.671%   $186.0453   $186.05   $186.05   $186.00  
  Purchase #6 $51.44   11.697%   $57.4569   $57.46   $57.45   $57.50  
  Purchase #7 $15.29   8.737%   $16.6259   $16.63   $16.65   $16.60  
  7 purchase totals = $936.70       $1,033.8992   $1,033.91   $1,033.95   $1,033.90