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 $234.95   13.666%   $267.0583   $267.06   $267.05   $267.10  
  Purchase #2 $72.99   8.648%   $79.3022   $79.30   $79.30   $79.30  
  Purchase #3 $146.47   6.242%   $155.6127   $155.61   $155.60   $155.60  
  Purchase #4 $5.79   9.206%   $6.323   $6.32   $6.30   $6.30  
  Purchase #5 $237.42   5.401%   $250.2431   $250.24   $250.25   $250.20  
  Purchase #6 $175.97   3.788%   $182.6357   $182.64   $182.65   $182.60  
  Purchase #7 $106.40   6.286%   $113.0883   $113.09   $113.10   $113.10  
  7 purchase totals = $979.99       $1,054.2633   $1,054.26   $1,054.25   $1,054.20