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 $61.57   3.378%   $63.6498   $63.65   $63.65   $63.60  
  Purchase #2 $159.32   4.664%   $166.7507   $166.75   $166.75   $166.80  
  Purchase #3 $55.90   12.798%   $63.0541   $63.05   $63.05   $63.10  
  Purchase #4 $19.62   8.750%   $21.3368   $21.34   $21.35   $21.30  
  Purchase #5 $209.94   13.145%   $237.5366   $237.54   $237.55   $237.50  
  Purchase #6 $81.93   4.161%   $85.3391   $85.34   $85.35   $85.30  
  Purchase #7 $56.81   5.581%   $59.9806   $59.98   $60.00   $60.00  
  7 purchase totals = $645.09       $697.6477   $697.65   $697.70   $697.60