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 $36.69   13.549%   $41.6611   $41.66   $41.65   $41.70  
  Purchase #2 $95.56   8.773%   $103.9435   $103.94   $103.95   $103.90  
  Purchase #3 $228.80   9.616%   $250.8014   $250.80   $250.80   $250.80  
  Purchase #4 $243.69   8.243%   $263.7774   $263.78   $263.80   $263.80  
  Purchase #5 $68.57   10.728%   $75.9262   $75.93   $75.95   $75.90  
  Purchase #6 $86.72   13.183%   $98.1523   $98.15   $98.15   $98.20  
  Purchase #7 $214.55   11.589%   $239.4142   $239.41   $239.40   $239.40  
  7 purchase totals = $974.58       $1,073.6761   $1,073.67   $1,073.70   $1,073.70