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 $183.76   11.563%   $205.0082   $205.01   $205.00   $205.00  
  Purchase #2 $102.26   11.435%   $113.9534   $113.95   $113.95   $114.00  
  Purchase #3 $180.40   3.274%   $186.3063   $186.31   $186.30   $186.30  
  Purchase #4 $78.98   7.397%   $84.8222   $84.82   $84.80   $84.80  
  Purchase #5 $82.73   11.170%   $91.9709   $91.97   $91.95   $92.00  
  Purchase #6 $61.33   11.493%   $68.3787   $68.38   $68.40   $68.40  
  Purchase #7 $225.58   5.432%   $237.8335   $237.83   $237.85   $237.80  
  7 purchase totals = $915.04       $988.2732   $988.27   $988.25   $988.30