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 $59.71   4.337%   $62.2996   $62.30   $62.30   $62.30  
  Purchase #2 $98.35   7.465%   $105.6918   $105.69   $105.70   $105.70  
  Purchase #3 $13.37   8.372%   $14.4893   $14.49   $14.50   $14.50  
  Purchase #4 $91.26   3.116%   $94.1037   $94.10   $94.10   $94.10  
  Purchase #5 $68.91   11.462%   $76.8085   $76.81   $76.80   $76.80  
  Purchase #6 $103.97   8.669%   $112.9832   $112.98   $113.00   $113.00  
  Purchase #7 $101.55   8.815%   $110.5016   $110.50   $110.50   $110.50  
  7 purchase totals = $537.12       $576.8777   $576.87   $576.90   $576.90