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 $207.84   13.334%   $235.5534   $235.55   $235.55   $235.60  
  Purchase #2 $65.38   11.566%   $72.9419   $72.94   $72.95   $72.90  
  Purchase #3 $240.65   3.179%   $248.3003   $248.30   $248.30   $248.30  
  Purchase #4 $138.70   7.203%   $148.6906   $148.69   $148.70   $148.70  
  Purchase #5 $138.50   11.536%   $154.4774   $154.48   $154.50   $154.50  
  Purchase #6 $101.54   12.250%   $113.9787   $113.98   $114.00   $114.00  
  Purchase #7 $214.51   9.386%   $234.6439   $234.64   $234.65   $234.60  
  7 purchase totals = $1,107.12       $1,208.5862   $1,208.58   $1,208.65   $1,208.60