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 $56.47   8.254%   $61.131   $61.13   $61.15   $61.10  
  Purchase #2 $102.93   9.197%   $112.3965   $112.40   $112.40   $112.40  
  Purchase #3 $139.53   12.574%   $157.0745   $157.07   $157.05   $157.10  
  Purchase #4 $54.39   4.869%   $57.0382   $57.04   $57.05   $57.00  
  Purchase #5 $163.35   7.755%   $176.0178   $176.02   $176.00   $176.00  
  Purchase #6 $98.70   12.152%   $110.694   $110.69   $110.70   $110.70  
  Purchase #7 $42.34   5.244%   $44.5603   $44.56   $44.55   $44.60  
  7 purchase totals = $657.71       $718.9123   $718.91   $718.90   $718.90