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 $93.54   6.458%   $99.5808   $99.58   $99.60   $99.60  
  Purchase #2 $223.97   10.827%   $248.2192   $248.22   $248.20   $248.20  
  Purchase #3 $81.94   5.813%   $86.7032   $86.70   $86.70   $86.70  
  Purchase #4 $61.51   5.468%   $64.8734   $64.87   $64.85   $64.90  
  Purchase #5 $127.97   6.291%   $136.0206   $136.02   $136.00   $136.00  
  Purchase #6 $29.74   11.706%   $33.2214   $33.22   $33.20   $33.20  
  Purchase #7 $246.58   7.495%   $265.0612   $265.06   $265.05   $265.10  
  7 purchase totals = $865.25       $933.6798   $933.67   $933.60   $933.70