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 $183.81   10.712%   $203.4997   $203.50   $203.50   $203.50  
  Purchase #2 $228.57   12.622%   $257.4201   $257.42   $257.40   $257.40  
  Purchase #3 $96.81   12.206%   $108.6266   $108.63   $108.65   $108.60  
  Purchase #4 $220.70   9.301%   $241.2273   $241.23   $241.25   $241.20  
  Purchase #5 $44.94   8.115%   $48.5869   $48.59   $48.60   $48.60  
  Purchase #6 $123.25   8.202%   $133.359   $133.36   $133.35   $133.40  
  Purchase #7 $169.40   9.560%   $185.5946   $185.59   $185.60   $185.60  
  7 purchase totals = $1,067.48       $1,178.3142   $1,178.32   $1,178.35   $1,178.30