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 $114.88   10.608%   $127.0665   $127.07   $127.05   $127.10  
  Purchase #2 $229.88   12.218%   $257.9667   $257.97   $257.95   $258.00  
  Purchase #3 $232.90   11.330%   $259.2876   $259.29   $259.30   $259.30  
  Purchase #4 $98.26   8.574%   $106.6848   $106.68   $106.70   $106.70  
  Purchase #5 $193.39   12.488%   $217.5405   $217.54   $217.55   $217.50  
  Purchase #6 $109.30   3.696%   $113.3397   $113.34   $113.35   $113.30  
  Purchase #7 $171.60   6.569%   $182.8724   $182.87   $182.85   $182.90  
  7 purchase totals = $1,150.21       $1,264.7582   $1,264.76   $1,264.75   $1,264.80