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 $226.73   8.767%   $246.6074   $246.61   $246.60   $246.60  
  Purchase #2 $49.27   4.316%   $51.3965   $51.40   $51.40   $51.40  
  Purchase #3 $117.87   6.113%   $125.0754   $125.08   $125.10   $125.10  
  Purchase #4 $38.76   9.597%   $42.4798   $42.48   $42.50   $42.50  
  Purchase #5 $32.85   6.268%   $34.909   $34.91   $34.90   $34.90  
  Purchase #6 $211.30   6.129%   $224.2506   $224.25   $224.25   $224.30  
  Purchase #7 $247.61   3.750%   $256.8954   $256.90   $256.90   $256.90  
  7 purchase totals = $924.39       $981.6141   $981.63   $981.65   $981.70