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 $53.32   8.327%   $57.76   $57.76   $57.75   $57.80  
  Purchase #2 $234.88   7.708%   $252.9846   $252.98   $253.00   $253.00  
  Purchase #3 $82.96   11.438%   $92.449   $92.45   $92.45   $92.40  
  Purchase #4 $71.92   5.732%   $76.0425   $76.04   $76.05   $76.00  
  Purchase #5 $127.26   5.391%   $134.1206   $134.12   $134.10   $134.10  
  Purchase #6 $239.89   5.532%   $253.1607   $253.16   $253.15   $253.20  
  Purchase #7 $91.27   9.801%   $100.2154   $100.22   $100.20   $100.20  
  7 purchase totals = $901.50       $966.7328   $966.73   $966.70   $966.70