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 $92.68   13.810%   $105.4791   $105.48   $105.50   $105.50  
  Purchase #2 $209.83   3.218%   $216.5823   $216.58   $216.60   $216.60  
  Purchase #3 $151.64   7.163%   $162.502   $162.50   $162.50   $162.50  
  Purchase #4 $188.45   3.826%   $195.6601   $195.66   $195.65   $195.70  
  Purchase #5 $115.62   13.268%   $130.9605   $130.96   $130.95   $131.00  
  Purchase #6 $65.43   12.623%   $73.6892   $73.69   $73.70   $73.70  
  Purchase #7 $119.78   12.496%   $134.7477   $134.75   $134.75   $134.70  
  7 purchase totals = $943.43       $1,019.6209   $1,019.62   $1,019.65   $1,019.70