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 $53.65   13.649%   $60.9727   $60.97   $60.95   $61.00  
  Purchase #2 $86.75   7.127%   $92.9327   $92.93   $92.95   $92.90  
  Purchase #3 $100.28   3.106%   $103.3947   $103.39   $103.40   $103.40  
  Purchase #4 $143.95   13.631%   $163.5718   $163.57   $163.55   $163.60  
  Purchase #5 $107.25   11.294%   $119.3628   $119.36   $119.35   $119.40  
  Purchase #6 $165.95   12.714%   $187.0489   $187.05   $187.05   $187.00  
  Purchase #7 $33.27   5.183%   $34.9944   $34.99   $35.00   $35.00  
  7 purchase totals = $691.10       $762.2780   $762.26   $762.25   $762.30