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 $55.84   7.327%   $59.9314   $59.93   $59.95   $59.90  
  Purchase #2 $117.94   7.373%   $126.6357   $126.64   $126.65   $126.60  
  Purchase #3 $114.54   8.262%   $124.0033   $124.00   $124.00   $124.00  
  Purchase #4 $207.50   10.137%   $228.5343   $228.53   $228.55   $228.50  
  Purchase #5 $226.95   3.122%   $234.0354   $234.04   $234.05   $234.00  
  Purchase #6 $121.82   4.551%   $127.364   $127.36   $127.35   $127.40  
  Purchase #7 $59.33   7.201%   $63.6024   $63.60   $63.60   $63.60  
  7 purchase totals = $903.92       $964.1065   $964.10   $964.15   $964.00