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 $189.70   9.385%   $207.5033   $207.50   $207.50   $207.50  
  Purchase #2 $114.53   6.216%   $121.6492   $121.65   $121.65   $121.60  
  Purchase #3 $163.98   12.197%   $183.9806   $183.98   $184.00   $184.00  
  Purchase #4 $245.54   6.714%   $262.0256   $262.03   $262.05   $262.00  
  Purchase #5 $46.49   8.584%   $50.4807   $50.48   $50.50   $50.50  
  Purchase #6 $117.26   3.773%   $121.6842   $121.68   $121.70   $121.70  
  Purchase #7 $21.45   3.772%   $22.2591   $22.26   $22.25   $22.30  
  7 purchase totals = $898.95       $969.5827   $969.58   $969.65   $969.60