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 $20.84   11.619%   $23.2614   $23.26   $23.25   $23.30  
  Purchase #2 $167.89   10.820%   $186.0557   $186.06   $186.05   $186.10  
  Purchase #3 $94.95   8.554%   $103.072   $103.07   $103.05   $103.10  
  Purchase #4 $157.28   8.160%   $170.114   $170.11   $170.10   $170.10  
  Purchase #5 $10.52   12.641%   $11.8498   $11.85   $11.85   $11.80  
  Purchase #6 $146.64   11.794%   $163.9347   $163.93   $163.95   $163.90  
  Purchase #7 $176.33   5.324%   $185.7178   $185.72   $185.70   $185.70  
  7 purchase totals = $774.45       $844.0054   $844.00   $843.95   $844.00