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 $56.92   8.172%   $61.5715   $61.57   $61.55   $61.60  
  Purchase #2 $93.37   5.547%   $98.5492   $98.55   $98.55   $98.50  
  Purchase #3 $216.42   13.464%   $245.5588   $245.56   $245.55   $245.60  
  Purchase #4 $64.57   13.745%   $73.4451   $73.45   $73.45   $73.40  
  Purchase #5 $189.53   13.812%   $215.7079   $215.71   $215.70   $215.70  
  Purchase #6 $203.62   6.271%   $216.389   $216.39   $216.40   $216.40  
  Purchase #7 $53.77   5.565%   $56.7623   $56.76   $56.75   $56.80  
  7 purchase totals = $878.20       $967.9838   $967.99   $967.95   $968.00