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   13.418%   $266.4756   $266.48   $266.50   $266.50  
  Purchase #2 $35.93   9.442%   $39.3225   $39.32   $39.30   $39.30  
  Purchase #3 $24.94   6.241%   $26.4965   $26.50   $26.50   $26.50  
  Purchase #4 $111.30   9.238%   $121.5819   $121.58   $121.60   $121.60  
  Purchase #5 $111.76   13.407%   $126.7437   $126.74   $126.75   $126.70  
  Purchase #6 $158.67   5.692%   $167.7015   $167.70   $167.70   $167.70  
  Purchase #7 $248.92   4.278%   $259.5688   $259.57   $259.55   $259.60  
  7 purchase totals = $926.47       $1,007.8905   $1,007.89   $1,007.90   $1,007.90