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 $227.96   8.792%   $248.0022   $248.00   $248.00   $248.00  
  Purchase #2 $226.38   8.104%   $244.7258   $244.73   $244.75   $244.70  
  Purchase #3 $10.93   5.697%   $11.5527   $11.55   $11.55   $11.60  
  Purchase #4 $194.26   4.636%   $203.2659   $203.27   $203.25   $203.30  
  Purchase #5 $27.77   3.264%   $28.6764   $28.68   $28.70   $28.70  
  Purchase #6 $190.75   10.517%   $210.8112   $210.81   $210.80   $210.80  
  Purchase #7 $108.25   5.567%   $114.2763   $114.28   $114.30   $114.30  
  7 purchase totals = $986.30       $1,061.3105   $1,061.32   $1,061.35   $1,061.40