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 $60.40   8.838%   $65.7382   $65.74   $65.75   $65.70  
  Purchase #2 $51.90   6.494%   $55.2704   $55.27   $55.25   $55.30  
  Purchase #3 $143.93   12.841%   $162.4121   $162.41   $162.40   $162.40  
  Purchase #4 $57.43   6.116%   $60.9424   $60.94   $60.95   $60.90  
  Purchase #5 $231.76   10.589%   $256.3011   $256.30   $256.30   $256.30  
  Purchase #6 $136.58   11.250%   $151.9453   $151.95   $151.95   $151.90  
  Purchase #7 $192.69   12.835%   $217.4218   $217.42   $217.40   $217.40  
  7 purchase totals = $874.69       $970.0313   $970.03   $970.00   $969.90