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 $88.89   5.243%   $93.5505   $93.55   $93.55   $93.60  
  Purchase #2 $129.39   9.529%   $141.7196   $141.72   $141.70   $141.70  
  Purchase #3 $49.69   10.695%   $55.0043   $55.00   $55.00   $55.00  
  Purchase #4 $179.85   7.278%   $192.9395   $192.94   $192.95   $192.90  
  Purchase #5 $183.63   10.146%   $202.2611   $202.26   $202.25   $202.30  
  Purchase #6 $237.85   10.852%   $263.6615   $263.66   $263.65   $263.70  
  Purchase #7 $44.63   8.411%   $48.3838   $48.38   $48.40   $48.40  
  7 purchase totals = $913.93       $997.5203   $997.51   $997.50   $997.60