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 $223.75   11.181%   $248.7675   $248.77   $248.75   $248.80  
  Purchase #2 $121.91   10.605%   $134.8386   $134.84   $134.85   $134.80  
  Purchase #3 $104.49   13.183%   $118.2649   $118.26   $118.25   $118.30  
  Purchase #4 $250.27   10.726%   $277.114   $277.11   $277.10   $277.10  
  Purchase #5 $230.92   11.201%   $256.7853   $256.79   $256.80   $256.80  
  Purchase #6 $119.78   11.433%   $133.4744   $133.47   $133.45   $133.50  
  Purchase #7 $59.26   13.641%   $67.3437   $67.34   $67.35   $67.30  
  7 purchase totals = $1,110.38       $1,236.5884   $1,236.58   $1,236.55   $1,236.60