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 $153.78   6.218%   $163.342   $163.34   $163.35   $163.30  
  Purchase #2 $235.77   11.571%   $263.0509   $263.05   $263.05   $263.10  
  Purchase #3 $65.74   9.156%   $71.7592   $71.76   $71.75   $71.80  
  Purchase #4 $23.61   10.512%   $26.0919   $26.09   $26.10   $26.10  
  Purchase #5 $162.35   12.493%   $182.6324   $182.63   $182.65   $182.60  
  Purchase #6 $111.50   4.518%   $116.5376   $116.54   $116.55   $116.50  
  Purchase #7 $129.69   12.664%   $146.1139   $146.11   $146.10   $146.10  
  7 purchase totals = $882.44       $969.5279   $969.52   $969.55   $969.50