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 $51.40   13.384%   $58.2794   $58.28   $58.30   $58.30  
  Purchase #2 $98.89   13.818%   $112.5546   $112.55   $112.55   $112.60  
  Purchase #3 $23.90   9.627%   $26.2009   $26.20   $26.20   $26.20  
  Purchase #4 $58.44   8.647%   $63.4933   $63.49   $63.50   $63.50  
  Purchase #5 $119.29   3.661%   $123.6572   $123.66   $123.65   $123.70  
  Purchase #6 $240.93   9.564%   $263.9725   $263.97   $263.95   $264.00  
  Purchase #7 $63.58   7.144%   $68.1222   $68.12   $68.10   $68.10  
  7 purchase totals = $656.43       $716.2801   $716.27   $716.25   $716.40