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 $215.61   9.239%   $235.5302   $235.53   $235.55   $235.50  
  Purchase #2 $63.38   3.183%   $65.3974   $65.40   $65.40   $65.40  
  Purchase #3 $82.36   13.392%   $93.3897   $93.39   $93.40   $93.40  
  Purchase #4 $138.92   3.213%   $143.3835   $143.38   $143.40   $143.40  
  Purchase #5 $113.99   3.537%   $118.0218   $118.02   $118.00   $118.00  
  Purchase #6 $226.71   6.562%   $241.5867   $241.59   $241.60   $241.60  
  Purchase #7 $89.84   9.853%   $98.6919   $98.69   $98.70   $98.70  
  7 purchase totals = $930.81       $996.0012   $996.00   $996.05   $996.00