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 $47.74   4.447%   $49.863   $49.86   $49.85   $49.90  
  Purchase #2 $214.62   8.546%   $232.9614   $232.96   $232.95   $233.00  
  Purchase #3 $83.33   7.849%   $89.8706   $89.87   $89.85   $89.90  
  Purchase #4 $25.65   6.425%   $27.298   $27.30   $27.30   $27.30  
  Purchase #5 $75.62   7.371%   $81.194   $81.19   $81.20   $81.20  
  Purchase #6 $241.48   10.597%   $267.0696   $267.07   $267.05   $267.10  
  Purchase #7 $208.40   12.807%   $235.0898   $235.09   $235.10   $235.10  
  7 purchase totals = $896.84       $983.3464   $983.34   $983.30   $983.50