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 $190.87   5.674%   $201.7   $201.70   $201.70   $201.70  
  Purchase #2 $107.38   13.269%   $121.6283   $121.63   $121.65   $121.60  
  Purchase #3 $110.76   8.241%   $119.8877   $119.89   $119.90   $119.90  
  Purchase #4 $205.61   10.359%   $226.9091   $226.91   $226.90   $226.90  
  Purchase #5 $38.38   8.258%   $41.5494   $41.55   $41.55   $41.50  
  Purchase #6 $99.87   4.380%   $104.2443   $104.24   $104.25   $104.20  
  Purchase #7 $40.90   13.433%   $46.3941   $46.39   $46.40   $46.40  
  7 purchase totals = $793.77       $862.3129   $862.31   $862.35   $862.20