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 $208.83   6.712%   $222.8467   $222.85   $222.85   $222.80  
  Purchase #2 $66.72   9.563%   $73.1004   $73.10   $73.10   $73.10  
  Purchase #3 $72.42   9.208%   $79.0884   $79.09   $79.10   $79.10  
  Purchase #4 $175.55   9.158%   $191.6269   $191.63   $191.65   $191.60  
  Purchase #5 $54.91   12.202%   $61.6101   $61.61   $61.60   $61.60  
  Purchase #6 $24.57   4.414%   $25.6545   $25.65   $25.65   $25.70  
  Purchase #7 $176.38   13.207%   $199.6745   $199.67   $199.65   $199.70  
  7 purchase totals = $779.38       $853.6015   $853.60   $853.60   $853.60