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 $107.25   11.320%   $119.3907   $119.39   $119.40   $119.40  
  Purchase #2 $88.38   3.465%   $91.4424   $91.44   $91.45   $91.40  
  Purchase #3 $174.87   6.343%   $185.962   $185.96   $185.95   $186.00  
  Purchase #4 $248.85   3.247%   $256.9302   $256.93   $256.95   $256.90  
  Purchase #5 $163.30   5.287%   $171.9337   $171.93   $171.95   $171.90  
  Purchase #6 $95.70   3.242%   $98.8026   $98.80   $98.80   $98.80  
  Purchase #7 $220.39   9.259%   $240.7959   $240.80   $240.80   $240.80  
  7 purchase totals = $1,098.74       $1,165.2575   $1,165.25   $1,165.30   $1,165.20