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 $207.92   11.504%   $231.8391   $231.84   $231.85   $231.80  
  Purchase #2 $173.87   6.158%   $184.5769   $184.58   $184.60   $184.60  
  Purchase #3 $106.71   12.336%   $119.8737   $119.87   $119.85   $119.90  
  Purchase #4 $76.86   12.128%   $86.1816   $86.18   $86.20   $86.20  
  Purchase #5 $162.80   8.783%   $177.0987   $177.10   $177.10   $177.10  
  Purchase #6 $43.94   7.820%   $47.3761   $47.38   $47.40   $47.40  
  Purchase #7 $176.53   8.109%   $190.8448   $190.84   $190.85   $190.80  
  7 purchase totals = $948.63       $1,037.7909   $1,037.79   $1,037.85   $1,037.80