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 $214.68   11.624%   $239.6344   $239.63   $239.65   $239.60  
  Purchase #2 $232.97   11.179%   $259.0137   $259.01   $259.00   $259.00  
  Purchase #3 $15.99   7.431%   $17.1782   $17.18   $17.20   $17.20  
  Purchase #4 $87.59   11.555%   $97.711   $97.71   $97.70   $97.70  
  Purchase #5 $112.33   5.387%   $118.3812   $118.38   $118.40   $118.40  
  Purchase #6 $42.61   6.716%   $45.4717   $45.47   $45.45   $45.50  
  Purchase #7 $203.51   9.456%   $222.7539   $222.75   $222.75   $222.80  
  7 purchase totals = $909.68       $1,000.1441   $1,000.13   $1,000.15   $1,000.20