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 $246.36   6.603%   $262.6272   $262.63   $262.65   $262.60  
  Purchase #2 $98.57   5.450%   $103.9421   $103.94   $103.95   $103.90  
  Purchase #3 $136.28   8.351%   $147.6607   $147.66   $147.65   $147.70  
  Purchase #4 $21.67   5.523%   $22.8668   $22.87   $22.85   $22.90  
  Purchase #5 $46.79   3.326%   $48.3462   $48.35   $48.35   $48.30  
  Purchase #6 $31.68   10.400%   $34.9747   $34.97   $34.95   $35.00  
  Purchase #7 $229.57   6.820%   $245.2267   $245.23   $245.25   $245.20  
  7 purchase totals = $810.92       $865.6444   $865.65   $865.65   $865.60