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 $23.59   13.446%   $26.7619   $26.76   $26.75   $26.80  
  Purchase #2 $210.83   8.463%   $228.6725   $228.67   $228.65   $228.70  
  Purchase #3 $76.31   8.550%   $82.8345   $82.83   $82.85   $82.80  
  Purchase #4 $136.56   13.344%   $154.7826   $154.78   $154.80   $154.80  
  Purchase #5 $5.74   5.238%   $6.0407   $6.04   $6.05   $6.00  
  Purchase #6 $184.65   8.797%   $200.8937   $200.89   $200.90   $200.90  
  Purchase #7 $52.55   6.145%   $55.7792   $55.78   $55.80   $55.80  
  7 purchase totals = $690.23       $755.7651   $755.75   $755.80   $755.80