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 $62.72   12.702%   $70.6867   $70.69   $70.70   $70.70  
  Purchase #2 $202.73   12.422%   $227.9131   $227.91   $227.90   $227.90  
  Purchase #3 $22.98   13.851%   $26.163   $26.16   $26.15   $26.20  
  Purchase #4 $163.75   5.478%   $172.7202   $172.72   $172.70   $172.70  
  Purchase #5 $65.47   11.766%   $73.1732   $73.17   $73.15   $73.20  
  Purchase #6 $140.51   8.380%   $152.2847   $152.28   $152.30   $152.30  
  Purchase #7 $228.95   4.454%   $239.1474   $239.15   $239.15   $239.10  
  7 purchase totals = $887.11       $962.0883   $962.08   $962.05   $962.10