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 $215.75   5.261%   $227.1006   $227.10   $227.10   $227.10  
  Purchase #2 $129.93   6.344%   $138.1728   $138.17   $138.15   $138.20  
  Purchase #3 $161.38   6.351%   $171.6292   $171.63   $171.65   $171.60  
  Purchase #4 $140.90   6.423%   $149.95   $149.95   $149.95   $150.00  
  Purchase #5 $163.33   5.249%   $171.9032   $171.90   $171.90   $171.90  
  Purchase #6 $15.58   4.801%   $16.328   $16.33   $16.35   $16.30  
  Purchase #7 $26.94   8.258%   $29.1647   $29.16   $29.15   $29.20  
  7 purchase totals = $853.81       $904.2485   $904.24   $904.25   $904.30