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 $166.64   11.705%   $186.1452   $186.15   $186.15   $186.10  
  Purchase #2 $108.78   5.212%   $114.4496   $114.45   $114.45   $114.40  
  Purchase #3 $137.76   8.822%   $149.9132   $149.91   $149.90   $149.90  
  Purchase #4 $59.96   12.442%   $67.4202   $67.42   $67.40   $67.40  
  Purchase #5 $183.94   13.517%   $208.8032   $208.80   $208.80   $208.80  
  Purchase #6 $224.33   10.149%   $247.0973   $247.10   $247.10   $247.10  
  Purchase #7 $129.71   9.228%   $141.6796   $141.68   $141.70   $141.70  
  7 purchase totals = $1,011.12       $1,115.5083   $1,115.51   $1,115.50   $1,115.40