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 $65.70   4.117%   $68.4049   $68.40   $68.40   $68.40  
  Purchase #2 $131.29   9.491%   $143.7507   $143.75   $143.75   $143.80  
  Purchase #3 $164.46   13.761%   $187.0913   $187.09   $187.10   $187.10  
  Purchase #4 $189.81   8.238%   $205.4465   $205.45   $205.45   $205.40  
  Purchase #5 $69.85   9.673%   $76.6066   $76.61   $76.60   $76.60  
  Purchase #6 $209.29   13.115%   $236.7384   $236.74   $236.75   $236.70  
  Purchase #7 $49.41   8.208%   $53.4656   $53.47   $53.45   $53.50  
  7 purchase totals = $879.81       $971.5040   $971.51   $971.50   $971.50