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 $242.33   8.796%   $263.6453   $263.65   $263.65   $263.60  
  Purchase #2 $34.85   9.453%   $38.1444   $38.14   $38.15   $38.10  
  Purchase #3 $76.61   12.205%   $85.9603   $85.96   $85.95   $86.00  
  Purchase #4 $211.85   4.453%   $221.2837   $221.28   $221.30   $221.30  
  Purchase #5 $119.86   10.619%   $132.5879   $132.59   $132.60   $132.60  
  Purchase #6 $98.28   4.249%   $102.4559   $102.46   $102.45   $102.50  
  Purchase #7 $174.38   5.786%   $184.4696   $184.47   $184.45   $184.50  
  7 purchase totals = $958.16       $1,028.5471   $1,028.55   $1,028.55   $1,028.60