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 $59.79   8.826%   $65.0671   $65.07   $65.05   $65.10  
  Purchase #2 $59.42   7.694%   $63.9918   $63.99   $64.00   $64.00  
  Purchase #3 $24.42   4.815%   $25.5958   $25.60   $25.60   $25.60  
  Purchase #4 $32.94   4.797%   $34.5201   $34.52   $34.50   $34.50  
  Purchase #5 $247.91   12.555%   $279.0351   $279.04   $279.05   $279.00  
  Purchase #6 $114.54   7.277%   $122.8751   $122.88   $122.90   $122.90  
  Purchase #7 $177.57   10.497%   $196.2095   $196.21   $196.20   $196.20  
  7 purchase totals = $716.59       $787.2945   $787.31   $787.30   $787.30