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 $191.81   3.763%   $199.0278   $199.03   $199.05   $199.00  
  Purchase #2 $56.59   3.107%   $58.3483   $58.35   $58.35   $58.30  
  Purchase #3 $215.99   8.743%   $234.874   $234.87   $234.85   $234.90  
  Purchase #4 $98.26   11.354%   $109.4164   $109.42   $109.40   $109.40  
  Purchase #5 $27.64   5.786%   $29.2393   $29.24   $29.25   $29.20  
  Purchase #6 $115.77   9.625%   $126.9129   $126.91   $126.90   $126.90  
  Purchase #7 $236.88   13.794%   $269.5552   $269.56   $269.55   $269.60  
  7 purchase totals = $942.94       $1,027.3739   $1,027.38   $1,027.35   $1,027.30