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 $164.66   13.539%   $186.9533   $186.95   $186.95   $187.00  
  Purchase #2 $182.98   10.536%   $202.2588   $202.26   $202.25   $202.30  
  Purchase #3 $240.61   10.256%   $265.287   $265.29   $265.30   $265.30  
  Purchase #4 $49.54   12.485%   $55.7251   $55.73   $55.75   $55.70  
  Purchase #5 $52.69   3.395%   $54.4788   $54.48   $54.50   $54.50  
  Purchase #6 $181.46   11.771%   $202.8197   $202.82   $202.80   $202.80  
  Purchase #7 $61.56   7.260%   $66.0293   $66.03   $66.05   $66.00  
  7 purchase totals = $933.50       $1,033.5520   $1,033.56   $1,033.60   $1,033.60