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 $60.27   13.224%   $68.2401   $68.24   $68.25   $68.20  
  Purchase #2 $138.86   13.326%   $157.3645   $157.36   $157.35   $157.40  
  Purchase #3 $24.61   6.348%   $26.1722   $26.17   $26.15   $26.20  
  Purchase #4 $150.59   6.270%   $160.032   $160.03   $160.05   $160.00  
  Purchase #5 $242.75   12.773%   $273.7565   $273.76   $273.75   $273.80  
  Purchase #6 $60.97   9.734%   $66.9048   $66.90   $66.90   $66.90  
  Purchase #7 $136.55   9.843%   $149.9906   $149.99   $150.00   $150.00  
  7 purchase totals = $814.60       $902.4607   $902.45   $902.45   $902.50