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 $86.88   12.257%   $97.5289   $97.53   $97.55   $97.50  
  Purchase #2 $165.61   8.786%   $180.1605   $180.16   $180.15   $180.20  
  Purchase #3 $247.46   7.381%   $265.725   $265.73   $265.75   $265.70  
  Purchase #4 $249.35   10.874%   $276.4643   $276.46   $276.45   $276.50  
  Purchase #5 $146.92   10.152%   $161.8353   $161.84   $161.85   $161.80  
  Purchase #6 $109.71   12.332%   $123.2394   $123.24   $123.25   $123.20  
  Purchase #7 $230.80   11.211%   $256.675   $256.68   $256.70   $256.70  
  7 purchase totals = $1,236.73       $1,361.6284   $1,361.64   $1,361.70   $1,361.60