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 $81.66   5.343%   $86.0231   $86.02   $86.00   $86.00  
  Purchase #2 $182.93   3.137%   $188.6685   $188.67   $188.65   $188.70  
  Purchase #3 $240.65   3.324%   $248.6492   $248.65   $248.65   $248.60  
  Purchase #4 $141.43   9.586%   $154.9875   $154.99   $155.00   $155.00  
  Purchase #5 $36.72   11.223%   $40.8411   $40.84   $40.85   $40.80  
  Purchase #6 $222.28   13.218%   $251.661   $251.66   $251.65   $251.70  
  Purchase #7 $123.71   12.537%   $139.2195   $139.22   $139.20   $139.20  
  7 purchase totals = $1,029.38       $1,110.0499   $1,110.05   $1,110.00   $1,110.00