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 $211.38   11.678%   $236.065   $236.07   $236.05   $236.10  
  Purchase #2 $123.88   5.707%   $130.9498   $130.95   $130.95   $130.90  
  Purchase #3 $184.96   8.256%   $200.2303   $200.23   $200.25   $200.20  
  Purchase #4 $244.58   8.122%   $264.4448   $264.44   $264.45   $264.40  
  Purchase #5 $241.66   9.592%   $264.84   $264.84   $264.85   $264.80  
  Purchase #6 $37.96   12.271%   $42.6181   $42.62   $42.60   $42.60  
  Purchase #7 $90.68   13.243%   $102.6888   $102.69   $102.70   $102.70  
  7 purchase totals = $1,135.10       $1,241.8368   $1,241.84   $1,241.85   $1,241.70