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 $186.46   8.655%   $202.5981   $202.60   $202.60   $202.60  
  Purchase #2 $134.63   5.146%   $141.5581   $141.56   $141.55   $141.60  
  Purchase #3 $165.89   13.647%   $188.529   $188.53   $188.55   $188.50  
  Purchase #4 $215.62   8.776%   $234.5428   $234.54   $234.55   $234.50  
  Purchase #5 $149.89   10.381%   $165.4501   $165.45   $165.45   $165.50  
  Purchase #6 $236.59   4.716%   $247.7476   $247.75   $247.75   $247.70  
  Purchase #7 $33.84   10.116%   $37.2633   $37.26   $37.25   $37.30  
  7 purchase totals = $1,122.92       $1,217.6890   $1,217.69   $1,217.70   $1,217.70