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 $61.99   9.581%   $67.9293   $67.93   $67.95   $67.90  
  Purchase #2 $17.81   12.762%   $20.0829   $20.08   $20.10   $20.10  
  Purchase #3 $209.86   11.527%   $234.0506   $234.05   $234.05   $234.10  
  Purchase #4 $82.59   5.638%   $87.2464   $87.25   $87.25   $87.20  
  Purchase #5 $190.90   4.827%   $200.1147   $200.11   $200.10   $200.10  
  Purchase #6 $102.65   10.308%   $113.2312   $113.23   $113.25   $113.20  
  Purchase #7 $231.97   3.386%   $239.8245   $239.82   $239.80   $239.80  
  7 purchase totals = $897.77       $962.4796   $962.47   $962.50   $962.40