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 $43.89   7.568%   $47.2116   $47.21   $47.20   $47.20  
  Purchase #2 $43.69   13.787%   $49.7135   $49.71   $49.70   $49.70  
  Purchase #3 $57.35   12.663%   $64.6122   $64.61   $64.60   $64.60  
  Purchase #4 $106.86   5.654%   $112.9019   $112.90   $112.90   $112.90  
  Purchase #5 $74.78   9.423%   $81.8265   $81.83   $81.85   $81.80  
  Purchase #6 $81.71   13.243%   $92.5309   $92.53   $92.55   $92.50  
  Purchase #7 $241.75   8.586%   $262.5067   $262.51   $262.50   $262.50  
  7 purchase totals = $650.03       $711.3033   $711.30   $711.30   $711.20