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 $60.93   7.558%   $65.5351   $65.54   $65.55   $65.50  
  Purchase #2 $132.94   6.412%   $141.4641   $141.46   $141.45   $141.50  
  Purchase #3 $116.65   4.180%   $121.526   $121.53   $121.55   $121.50  
  Purchase #4 $11.75   12.181%   $13.1813   $13.18   $13.20   $13.20  
  Purchase #5 $222.99   12.437%   $250.7233   $250.72   $250.70   $250.70  
  Purchase #6 $152.42   8.658%   $165.6165   $165.62   $165.60   $165.60  
  Purchase #7 $196.53   6.246%   $208.8053   $208.81   $208.80   $208.80  
  7 purchase totals = $894.21       $966.8516   $966.86   $966.85   $966.80