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 $76.60   11.709%   $85.5691   $85.57   $85.55   $85.60  
  Purchase #2 $177.31   4.148%   $184.6648   $184.66   $184.65   $184.70  
  Purchase #3 $72.31   6.781%   $77.2133   $77.21   $77.20   $77.20  
  Purchase #4 $73.41   3.567%   $76.0285   $76.03   $76.05   $76.00  
  Purchase #5 $112.80   3.423%   $116.6611   $116.66   $116.65   $116.70  
  Purchase #6 $239.63   4.326%   $249.9964   $250.00   $250.00   $250.00  
  Purchase #7 $136.95   3.722%   $142.0473   $142.05   $142.05   $142.00  
  7 purchase totals = $889.01       $932.1805   $932.18   $932.15   $932.20