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 $164.25   8.589%   $178.3574   $178.36   $178.35   $178.40  
  Purchase #2 $105.31   9.253%   $115.0543   $115.05   $115.05   $115.10  
  Purchase #3 $232.47   11.644%   $259.5388   $259.54   $259.55   $259.50  
  Purchase #4 $143.78   9.664%   $157.6749   $157.67   $157.65   $157.70  
  Purchase #5 $154.69   8.722%   $168.1821   $168.18   $168.20   $168.20  
  Purchase #6 $74.92   9.688%   $82.1782   $82.18   $82.20   $82.20  
  Purchase #7 $44.59   7.153%   $47.7795   $47.78   $47.80   $47.80  
  7 purchase totals = $920.01       $1,008.7652   $1,008.76   $1,008.80   $1,008.90