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 $229.96   12.650%   $259.0499   $259.05   $259.05   $259.00  
  Purchase #2 $46.33   7.290%   $49.7075   $49.71   $49.70   $49.70  
  Purchase #3 $121.43   10.704%   $134.4279   $134.43   $134.45   $134.40  
  Purchase #4 $249.77   8.676%   $271.44   $271.44   $271.45   $271.40  
  Purchase #5 $85.86   12.631%   $96.705   $96.71   $96.70   $96.70  
  Purchase #6 $147.49   3.496%   $152.6463   $152.65   $152.65   $152.60  
  Purchase #7 $197.28   4.187%   $205.5401   $205.54   $205.55   $205.50  
  7 purchase totals = $1,078.12       $1,169.5167   $1,169.53   $1,169.55   $1,169.30