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 $200.38   4.117%   $208.6296   $208.63   $208.65   $208.60  
  Purchase #2 $56.85   6.860%   $60.7499   $60.75   $60.75   $60.70  
  Purchase #3 $91.41   4.704%   $95.7099   $95.71   $95.70   $95.70  
  Purchase #4 $173.93   11.167%   $193.3528   $193.35   $193.35   $193.40  
  Purchase #5 $167.57   9.309%   $183.1691   $183.17   $183.15   $183.20  
  Purchase #6 $220.63   6.426%   $234.8077   $234.81   $234.80   $234.80  
  Purchase #7 $68.82   8.589%   $74.7309   $74.73   $74.75   $74.70  
  7 purchase totals = $979.59       $1,051.1499   $1,051.15   $1,051.15   $1,051.10