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 $105.63   8.448%   $114.5536   $114.55   $114.55   $114.60  
  Purchase #2 $20.29   11.660%   $22.6558   $22.66   $22.65   $22.70  
  Purchase #3 $38.69   5.365%   $40.7657   $40.77   $40.75   $40.80  
  Purchase #4 $51.93   8.225%   $56.2012   $56.20   $56.20   $56.20  
  Purchase #5 $59.79   8.718%   $65.0025   $65.00   $65.00   $65.00  
  Purchase #6 $76.55   10.815%   $84.8289   $84.83   $84.85   $84.80  
  Purchase #7 $166.78   8.764%   $181.3966   $181.40   $181.40   $181.40  
  7 purchase totals = $519.66       $565.4043   $565.41   $565.40   $565.50