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 $232.53   11.788%   $259.9406   $259.94   $259.95   $259.90  
  Purchase #2 $158.52   11.442%   $176.6579   $176.66   $176.65   $176.70  
  Purchase #3 $225.30   5.119%   $236.8331   $236.83   $236.85   $236.80  
  Purchase #4 $224.39   8.233%   $242.864   $242.86   $242.85   $242.90  
  Purchase #5 $161.73   12.852%   $182.5155   $182.52   $182.50   $182.50  
  Purchase #6 $34.48   4.304%   $35.964   $35.96   $35.95   $36.00  
  Purchase #7 $163.25   12.152%   $183.0881   $183.09   $183.10   $183.10  
  7 purchase totals = $1,200.20       $1,317.8632   $1,317.86   $1,317.85   $1,317.90