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 $200.68   10.773%   $222.2993   $222.30   $222.30   $222.30  
  Purchase #2 $220.85   6.137%   $234.4036   $234.40   $234.40   $234.40  
  Purchase #3 $84.70   8.828%   $92.1773   $92.18   $92.20   $92.20  
  Purchase #4 $46.69   12.737%   $52.6369   $52.64   $52.65   $52.60  
  Purchase #5 $249.82   8.330%   $270.63   $270.63   $270.65   $270.60  
  Purchase #6 $163.37   11.545%   $182.2311   $182.23   $182.25   $182.20  
  Purchase #7 $160.49   5.357%   $169.0874   $169.09   $169.10   $169.10  
  7 purchase totals = $1,126.60       $1,223.4656   $1,223.47   $1,223.55   $1,223.40