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 $208.50   13.406%   $236.4515   $236.45   $236.45   $236.50  
  Purchase #2 $210.90   3.293%   $217.8449   $217.84   $217.85   $217.80  
  Purchase #3 $76.81   9.691%   $84.2537   $84.25   $84.25   $84.30  
  Purchase #4 $58.38   10.852%   $64.7154   $64.72   $64.70   $64.70  
  Purchase #5 $215.61   6.643%   $229.933   $229.93   $229.95   $229.90  
  Purchase #6 $207.99   5.298%   $219.0093   $219.01   $219.00   $219.00  
  Purchase #7 $35.63   7.642%   $38.3528   $38.35   $38.35   $38.40  
  7 purchase totals = $1,013.82       $1,090.5606   $1,090.55   $1,090.55   $1,090.60