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 $84.59   8.268%   $91.5839   $91.58   $91.60   $91.60  
  Purchase #2 $32.99   9.682%   $36.1841   $36.18   $36.20   $36.20  
  Purchase #3 $85.25   12.341%   $95.7707   $95.77   $95.75   $95.80  
  Purchase #4 $33.50   3.753%   $34.7573   $34.76   $34.75   $34.80  
  Purchase #5 $242.92   7.797%   $261.8605   $261.86   $261.85   $261.90  
  Purchase #6 $68.36   3.126%   $70.4969   $70.50   $70.50   $70.50  
  Purchase #7 $146.36   13.303%   $165.8303   $165.83   $165.85   $165.80  
  7 purchase totals = $693.97       $756.4837   $756.48   $756.50   $756.60