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 $56.53   11.838%   $63.222   $63.22   $63.20   $63.20  
  Purchase #2 $72.42   3.457%   $74.9236   $74.92   $74.90   $74.90  
  Purchase #3 $164.89   12.741%   $185.8986   $185.90   $185.90   $185.90  
  Purchase #4 $112.72   7.865%   $121.5854   $121.59   $121.60   $121.60  
  Purchase #5 $224.92   9.212%   $245.6396   $245.64   $245.65   $245.60  
  Purchase #6 $196.48   5.690%   $207.6597   $207.66   $207.65   $207.70  
  Purchase #7 $81.62   5.137%   $85.8128   $85.81   $85.80   $85.80  
  7 purchase totals = $909.58       $984.7417   $984.74   $984.70   $984.70