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 $74.87   10.797%   $82.9537   $82.95   $82.95   $83.00  
  Purchase #2 $222.31   8.229%   $240.6039   $240.60   $240.60   $240.60  
  Purchase #3 $241.89   9.845%   $265.7041   $265.70   $265.70   $265.70  
  Purchase #4 $151.42   7.630%   $162.9733   $162.97   $162.95   $163.00  
  Purchase #5 $203.83   11.185%   $226.6284   $226.63   $226.65   $226.60  
  Purchase #6 $235.54   9.728%   $258.4533   $258.45   $258.45   $258.50  
  Purchase #7 $49.54   6.668%   $52.8433   $52.84   $52.85   $52.80  
  7 purchase totals = $1,179.40       $1,290.1600   $1,290.14   $1,290.15   $1,290.20