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 $55.44   11.789%   $61.9758   $61.98   $62.00   $62.00  
  Purchase #2 $76.90   9.218%   $83.9886   $83.99   $84.00   $84.00  
  Purchase #3 $103.56   11.444%   $115.4114   $115.41   $115.40   $115.40  
  Purchase #4 $69.28   13.128%   $78.3751   $78.38   $78.40   $78.40  
  Purchase #5 $142.64   4.205%   $148.638   $148.64   $148.65   $148.60  
  Purchase #6 $73.57   9.549%   $80.5952   $80.60   $80.60   $80.60  
  Purchase #7 $78.73   7.138%   $84.3497   $84.35   $84.35   $84.30  
  7 purchase totals = $600.12       $653.3338   $653.35   $653.40   $653.30