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 $103.55   10.596%   $114.5222   $114.52   $114.50   $114.50  
  Purchase #2 $214.77   6.268%   $228.2318   $228.23   $228.25   $228.20  
  Purchase #3 $62.99   4.828%   $66.0312   $66.03   $66.05   $66.00  
  Purchase #4 $75.52   10.547%   $83.4851   $83.49   $83.50   $83.50  
  Purchase #5 $217.84   5.250%   $229.2766   $229.28   $229.30   $229.30  
  Purchase #6 $182.30   3.353%   $188.4125   $188.41   $188.40   $188.40  
  Purchase #7 $50.86   4.553%   $53.1757   $53.18   $53.20   $53.20  
  7 purchase totals = $907.83       $963.1351   $963.14   $963.20   $963.10