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 $238.71   10.400%   $263.5358   $263.54   $263.55   $263.50  
  Purchase #2 $41.60   13.189%   $47.0866   $47.09   $47.10   $47.10  
  Purchase #3 $24.53   3.653%   $25.4261   $25.43   $25.45   $25.40  
  Purchase #4 $155.99   4.419%   $162.8832   $162.88   $162.90   $162.90  
  Purchase #5 $123.73   5.491%   $130.524   $130.52   $130.50   $130.50  
  Purchase #6 $115.67   13.370%   $131.1351   $131.14   $131.15   $131.10  
  Purchase #7 $149.99   4.331%   $156.4861   $156.49   $156.50   $156.50  
  7 purchase totals = $850.22       $917.0769   $917.09   $917.15   $917.00