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 $59.42   4.389%   $62.0279   $62.03   $62.05   $62.00  
  Purchase #2 $121.27   6.629%   $129.309   $129.31   $129.30   $129.30  
  Purchase #3 $134.32   6.394%   $142.9084   $142.91   $142.90   $142.90  
  Purchase #4 $26.48   4.830%   $27.759   $27.76   $27.75   $27.80  
  Purchase #5 $167.65   4.532%   $175.2479   $175.25   $175.25   $175.20  
  Purchase #6 $232.66   3.322%   $240.389   $240.39   $240.40   $240.40  
  Purchase #7 $17.28   10.852%   $19.1552   $19.16   $19.15   $19.20  
  7 purchase totals = $759.08       $796.7964   $796.81   $796.80   $796.80