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 $49.46   6.669%   $52.7585   $52.76   $52.75   $52.80  
  Purchase #2 $236.32   3.124%   $243.7026   $243.70   $243.70   $243.70  
  Purchase #3 $211.68   5.364%   $223.0345   $223.03   $223.05   $223.00  
  Purchase #4 $19.37   4.500%   $20.2417   $20.24   $20.25   $20.20  
  Purchase #5 $38.47   9.329%   $42.0589   $42.06   $42.05   $42.10  
  Purchase #6 $227.87   10.827%   $252.5415   $252.54   $252.55   $252.50  
  Purchase #7 $245.63   6.279%   $261.0531   $261.05   $261.05   $261.10  
  7 purchase totals = $1,028.80       $1,095.3908   $1,095.38   $1,095.40   $1,095.40