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 $53.41   11.574%   $59.5917   $59.59   $59.60   $59.60  
  Purchase #2 $208.38   7.621%   $224.2606   $224.26   $224.25   $224.30  
  Purchase #3 $129.74   8.762%   $141.1078   $141.11   $141.10   $141.10  
  Purchase #4 $234.43   8.326%   $253.9486   $253.95   $253.95   $253.90  
  Purchase #5 $23.89   11.479%   $26.6323   $26.63   $26.65   $26.60  
  Purchase #6 $90.94   6.261%   $96.6338   $96.63   $96.65   $96.60  
  Purchase #7 $5.68   3.754%   $5.8932   $5.89   $5.90   $5.90  
  7 purchase totals = $746.47       $808.0680   $808.06   $808.10   $808.00