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 $84.49   3.203%   $87.1962   $87.20   $87.20   $87.20  
  Purchase #2 $52.95   7.777%   $57.0679   $57.07   $57.05   $57.10  
  Purchase #3 $64.93   12.401%   $72.982   $72.98   $73.00   $73.00  
  Purchase #4 $21.93   10.358%   $24.2015   $24.20   $24.20   $24.20  
  Purchase #5 $80.69   7.348%   $86.6191   $86.62   $86.60   $86.60  
  Purchase #6 $208.99   6.791%   $223.1825   $223.18   $223.20   $223.20  
  Purchase #7 $9.66   3.648%   $10.0124   $10.01   $10.00   $10.00  
  7 purchase totals = $523.64       $561.2616   $561.26   $561.25   $561.30