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 $221.97   11.518%   $247.5365   $247.54   $247.55   $247.50  
  Purchase #2 $232.59   13.278%   $263.4733   $263.47   $263.45   $263.50  
  Purchase #3 $39.64   9.475%   $43.3959   $43.40   $43.40   $43.40  
  Purchase #4 $41.46   7.338%   $44.5023   $44.50   $44.50   $44.50  
  Purchase #5 $23.53   10.764%   $26.0628   $26.06   $26.05   $26.10  
  Purchase #6 $176.68   3.619%   $183.074   $183.07   $183.05   $183.10  
  Purchase #7 $12.70   11.582%   $14.1709   $14.17   $14.15   $14.20  
  7 purchase totals = $748.57       $822.2157   $822.21   $822.15   $822.30