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 $238.36   12.363%   $267.8284   $267.83   $267.85   $267.80  
  Purchase #2 $105.66   6.541%   $112.5712   $112.57   $112.55   $112.60  
  Purchase #3 $221.36   6.786%   $236.3815   $236.38   $236.40   $236.40  
  Purchase #4 $37.33   9.686%   $40.9458   $40.95   $40.95   $40.90  
  Purchase #5 $200.69   3.465%   $207.6439   $207.64   $207.65   $207.60  
  Purchase #6 $115.96   5.301%   $122.107   $122.11   $122.10   $122.10  
  Purchase #7 $109.85   4.480%   $114.7713   $114.77   $114.75   $114.80  
  7 purchase totals = $1,029.21       $1,102.2491   $1,102.25   $1,102.25   $1,102.20