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 $34.34   12.448%   $38.6146   $38.61   $38.60   $38.60  
  Purchase #2 $159.47   10.610%   $176.3898   $176.39   $176.40   $176.40  
  Purchase #3 $216.69   3.520%   $224.3175   $224.32   $224.30   $224.30  
  Purchase #4 $24.81   12.701%   $27.9611   $27.96   $27.95   $28.00  
  Purchase #5 $142.81   9.221%   $155.9785   $155.98   $156.00   $156.00  
  Purchase #6 $95.57   5.337%   $100.6706   $100.67   $100.65   $100.70  
  Purchase #7 $23.77   3.328%   $24.5611   $24.56   $24.55   $24.60  
  7 purchase totals = $697.46       $748.4932   $748.49   $748.45   $748.60