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 $232.46   13.566%   $263.9955   $264.00   $264.00   $264.00  
  Purchase #2 $95.72   3.357%   $98.9333   $98.93   $98.95   $98.90  
  Purchase #3 $114.70   11.787%   $128.2197   $128.22   $128.20   $128.20  
  Purchase #4 $117.56   9.242%   $128.4249   $128.42   $128.40   $128.40  
  Purchase #5 $175.59   3.552%   $181.827   $181.83   $181.85   $181.80  
  Purchase #6 $32.73   4.782%   $34.2951   $34.30   $34.30   $34.30  
  Purchase #7 $170.61   10.742%   $188.9369   $188.94   $188.95   $188.90  
  7 purchase totals = $939.37       $1,024.6324   $1,024.64   $1,024.65   $1,024.50