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 $248.60   7.397%   $266.9889   $266.99   $267.00   $267.00  
  Purchase #2 $52.95   4.607%   $55.3894   $55.39   $55.40   $55.40  
  Purchase #3 $166.68   9.693%   $182.8363   $182.84   $182.85   $182.80  
  Purchase #4 $37.85   7.714%   $40.7697   $40.77   $40.75   $40.80  
  Purchase #5 $58.36   9.201%   $63.7297   $63.73   $63.75   $63.70  
  Purchase #6 $151.36   8.557%   $164.3119   $164.31   $164.30   $164.30  
  Purchase #7 $176.83   6.644%   $188.5786   $188.58   $188.60   $188.60  
  7 purchase totals = $892.63       $962.6045   $962.61   $962.65   $962.60