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 $136.48   12.180%   $153.1033   $153.10   $153.10   $153.10  
  Purchase #2 $209.91   6.262%   $223.0546   $223.05   $223.05   $223.10  
  Purchase #3 $82.32   11.773%   $92.0115   $92.01   $92.00   $92.00  
  Purchase #4 $226.63   3.519%   $234.6051   $234.61   $234.60   $234.60  
  Purchase #5 $179.81   11.808%   $201.042   $201.04   $201.05   $201.00  
  Purchase #6 $71.38   7.616%   $76.8163   $76.82   $76.80   $76.80  
  Purchase #7 $70.83   5.481%   $74.7122   $74.71   $74.70   $74.70  
  7 purchase totals = $977.36       $1,055.3450   $1,055.34   $1,055.30   $1,055.30