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 $182.51   13.526%   $207.1963   $207.20   $207.20   $207.20  
  Purchase #2 $93.36   4.480%   $97.5425   $97.54   $97.55   $97.50  
  Purchase #3 $50.83   5.460%   $53.6053   $53.61   $53.60   $53.60  
  Purchase #4 $73.56   13.609%   $83.5708   $83.57   $83.55   $83.60  
  Purchase #5 $215.38   12.305%   $241.8825   $241.88   $241.90   $241.90  
  Purchase #6 $153.32   13.612%   $174.1899   $174.19   $174.20   $174.20  
  Purchase #7 $81.34   9.831%   $89.3365   $89.34   $89.35   $89.30  
  7 purchase totals = $850.30       $947.3238   $947.33   $947.35   $947.30