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 $154.83   8.766%   $168.4024   $168.40   $168.40   $168.40  
  Purchase #2 $223.29   9.247%   $243.9376   $243.94   $243.95   $243.90  
  Purchase #3 $105.59   12.225%   $118.4984   $118.50   $118.50   $118.50  
  Purchase #4 $24.75   5.696%   $26.1598   $26.16   $26.15   $26.20  
  Purchase #5 $35.62   9.579%   $39.032   $39.03   $39.05   $39.00  
  Purchase #6 $118.94   11.804%   $132.9797   $132.98   $133.00   $133.00  
  Purchase #7 $92.95   4.421%   $97.0593   $97.06   $97.05   $97.10  
  7 purchase totals = $755.97       $826.0692   $826.07   $826.10   $826.10