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 $146.76   13.783%   $166.9879   $166.99   $167.00   $167.00  
  Purchase #2 $239.31   4.563%   $250.2297   $250.23   $250.25   $250.20  
  Purchase #3 $194.48   6.867%   $207.8349   $207.83   $207.85   $207.80  
  Purchase #4 $48.28   7.373%   $51.8397   $51.84   $51.85   $51.80  
  Purchase #5 $213.53   8.167%   $230.969   $230.97   $230.95   $231.00  
  Purchase #6 $229.54   13.221%   $259.8875   $259.89   $259.90   $259.90  
  Purchase #7 $221.55   8.787%   $241.0176   $241.02   $241.00   $241.00  
  7 purchase totals = $1,293.45       $1,408.7663   $1,408.77   $1,408.80   $1,408.70