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 $61.99   10.258%   $68.3489   $68.35   $68.35   $68.30  
  Purchase #2 $134.68   4.727%   $141.0463   $141.05   $141.05   $141.00  
  Purchase #3 $175.48   3.470%   $181.5692   $181.57   $181.55   $181.60  
  Purchase #4 $70.77   8.173%   $76.554   $76.55   $76.55   $76.60  
  Purchase #5 $147.79   13.713%   $168.0564   $168.06   $168.05   $168.10  
  Purchase #6 $5.82   12.285%   $6.535   $6.54   $6.55   $6.50  
  Purchase #7 $142.95   10.535%   $158.0098   $158.01   $158.00   $158.00  
  7 purchase totals = $739.48       $800.1196   $800.13   $800.10   $800.10