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 $56.83   10.118%   $62.5801   $62.58   $62.60   $62.60  
  Purchase #2 $66.63   7.588%   $71.6859   $71.69   $71.70   $71.70  
  Purchase #3 $240.88   4.642%   $252.0616   $252.06   $252.05   $252.10  
  Purchase #4 $24.86   6.765%   $26.5418   $26.54   $26.55   $26.50  
  Purchase #5 $8.36   13.454%   $9.4848   $9.48   $9.50   $9.50  
  Purchase #6 $74.77   13.599%   $84.938   $84.94   $84.95   $84.90  
  Purchase #7 $141.69   13.131%   $160.2953   $160.30   $160.30   $160.30  
  7 purchase totals = $614.02       $667.5875   $667.59   $667.65   $667.60