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 $239.53   13.780%   $272.5372   $272.54   $272.55   $272.50  
  Purchase #2 $132.51   11.445%   $147.6758   $147.68   $147.70   $147.70  
  Purchase #3 $121.98   5.305%   $128.451   $128.45   $128.45   $128.50  
  Purchase #4 $24.40   7.555%   $26.2434   $26.24   $26.25   $26.20  
  Purchase #5 $85.55   12.494%   $96.2386   $96.24   $96.25   $96.20  
  Purchase #6 $34.59   9.849%   $37.9968   $38.00   $38.00   $38.00  
  Purchase #7 $78.99   8.396%   $85.622   $85.62   $85.60   $85.60  
  7 purchase totals = $717.55       $794.7648   $794.77   $794.80   $794.70