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 $98.78   10.149%   $108.8052   $108.81   $108.80   $108.80  
  Purchase #2 $200.52   11.180%   $222.9381   $222.94   $222.95   $222.90  
  Purchase #3 $57.36   11.738%   $64.0929   $64.09   $64.10   $64.10  
  Purchase #4 $244.56   3.438%   $252.968   $252.97   $252.95   $253.00  
  Purchase #5 $23.86   11.361%   $26.5707   $26.57   $26.55   $26.60  
  Purchase #6 $37.31   4.597%   $39.0251   $39.03   $39.05   $39.00  
  Purchase #7 $37.85   8.785%   $41.1751   $41.18   $41.20   $41.20  
  7 purchase totals = $700.24       $755.5751   $755.59   $755.60   $755.60