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 $76.59   12.424%   $86.1055   $86.11   $86.10   $86.10  
  Purchase #2 $103.48   10.281%   $114.1188   $114.12   $114.10   $114.10  
  Purchase #3 $207.93   6.522%   $221.4912   $221.49   $221.50   $221.50  
  Purchase #4 $84.80   7.706%   $91.3347   $91.33   $91.35   $91.30  
  Purchase #5 $63.76   4.800%   $66.8205   $66.82   $66.80   $66.80  
  Purchase #6 $13.61   7.674%   $14.6544   $14.65   $14.65   $14.70  
  Purchase #7 $226.60   4.804%   $237.4859   $237.49   $237.50   $237.50  
  7 purchase totals = $776.77       $832.0110   $832.01   $832.00   $832.00