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 $170.88   13.331%   $193.66   $193.66   $193.65   $193.70  
  Purchase #2 $61.69   6.807%   $65.8892   $65.89   $65.90   $65.90  
  Purchase #3 $227.31   13.234%   $257.3922   $257.39   $257.40   $257.40  
  Purchase #4 $179.25   5.119%   $188.4258   $188.43   $188.45   $188.40  
  Purchase #5 $55.53   8.649%   $60.3328   $60.33   $60.35   $60.30  
  Purchase #6 $166.63   6.824%   $178.0008   $178.00   $178.00   $178.00  
  Purchase #7 $226.67   9.782%   $248.8429   $248.84   $248.85   $248.80  
  7 purchase totals = $1,087.96       $1,192.5437   $1,192.54   $1,192.60   $1,192.50