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 $60.36   4.139%   $62.8583   $62.86   $62.85   $62.90  
  Purchase #2 $15.57   6.825%   $16.6327   $16.63   $16.65   $16.60  
  Purchase #3 $27.92   4.159%   $29.0812   $29.08   $29.10   $29.10  
  Purchase #4 $76.47   8.824%   $83.2177   $83.22   $83.20   $83.20  
  Purchase #5 $154.98   8.493%   $168.1425   $168.14   $168.15   $168.10  
  Purchase #6 $246.70   9.829%   $270.9481   $270.95   $270.95   $270.90  
  Purchase #7 $220.93   7.127%   $236.6757   $236.68   $236.70   $236.70  
  7 purchase totals = $802.93       $867.5562   $867.56   $867.60   $867.50