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 $89.93   7.394%   $96.5794   $96.58   $96.60   $96.60  
  Purchase #2 $58.32   3.602%   $60.4207   $60.42   $60.40   $60.40  
  Purchase #3 $202.77   6.397%   $215.7412   $215.74   $215.75   $215.70  
  Purchase #4 $61.92   5.515%   $65.3349   $65.33   $65.35   $65.30  
  Purchase #5 $34.95   7.582%   $37.5999   $37.60   $37.60   $37.60  
  Purchase #6 $113.53   11.771%   $126.8936   $126.89   $126.90   $126.90  
  Purchase #7 $226.74   5.709%   $239.6846   $239.68   $239.70   $239.70  
  7 purchase totals = $788.16       $842.2543   $842.24   $842.30   $842.20