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 $24.51   9.819%   $26.9166   $26.92   $26.90   $26.90  
  Purchase #2 $167.97   3.518%   $173.8792   $173.88   $173.90   $173.90  
  Purchase #3 $231.80   12.766%   $261.3916   $261.39   $261.40   $261.40  
  Purchase #4 $51.27   10.514%   $56.6605   $56.66   $56.65   $56.70  
  Purchase #5 $147.45   3.744%   $152.9705   $152.97   $152.95   $153.00  
  Purchase #6 $127.95   3.553%   $132.4961   $132.50   $132.50   $132.50  
  Purchase #7 $141.71   8.353%   $153.547   $153.55   $153.55   $153.50  
  7 purchase totals = $892.66       $957.8615   $957.87   $957.85   $957.90