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 $74.73   13.552%   $84.8574   $84.86   $84.85   $84.90  
  Purchase #2 $151.58   8.483%   $164.4385   $164.44   $164.45   $164.40  
  Purchase #3 $46.65   7.197%   $50.0074   $50.01   $50.00   $50.00  
  Purchase #4 $95.77   8.669%   $104.0723   $104.07   $104.05   $104.10  
  Purchase #5 $167.92   8.405%   $182.0337   $182.03   $182.05   $182.00  
  Purchase #6 $164.89   5.646%   $174.1997   $174.20   $174.20   $174.20  
  Purchase #7 $247.52   7.597%   $266.3241   $266.32   $266.30   $266.30  
  7 purchase totals = $949.06       $1,025.9331   $1,025.93   $1,025.90   $1,025.90