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 $161.87   8.844%   $176.1858   $176.19   $176.20   $176.20  
  Purchase #2 $27.42   4.717%   $28.7134   $28.71   $28.70   $28.70  
  Purchase #3 $227.32   11.250%   $252.8935   $252.89   $252.90   $252.90  
  Purchase #4 $74.33   11.849%   $83.1374   $83.14   $83.15   $83.10  
  Purchase #5 $90.28   5.476%   $95.2237   $95.22   $95.20   $95.20  
  Purchase #6 $245.86   5.181%   $258.598   $258.60   $258.60   $258.60  
  Purchase #7 $113.83   4.156%   $118.5608   $118.56   $118.55   $118.60  
  7 purchase totals = $940.91       $1,013.3126   $1,013.31   $1,013.30   $1,013.30