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 $232.83   13.848%   $265.0723   $265.07   $265.05   $265.10  
  Purchase #2 $118.87   5.143%   $124.9835   $124.98   $125.00   $125.00  
  Purchase #3 $149.97   3.820%   $155.6989   $155.70   $155.70   $155.70  
  Purchase #4 $203.32   6.236%   $215.999   $216.00   $216.00   $216.00  
  Purchase #5 $223.31   8.513%   $242.3204   $242.32   $242.30   $242.30  
  Purchase #6 $79.62   3.167%   $82.1416   $82.14   $82.15   $82.10  
  Purchase #7 $66.77   9.410%   $73.0531   $73.05   $73.05   $73.10  
  7 purchase totals = $1,074.69       $1,159.2688   $1,159.26   $1,159.25   $1,159.30