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 $26.83   4.340%   $27.9944   $27.99   $28.00   $28.00  
  Purchase #2 $108.67   5.819%   $114.9935   $114.99   $115.00   $115.00  
  Purchase #3 $142.98   9.264%   $156.2257   $156.23   $156.25   $156.20  
  Purchase #4 $129.69   8.378%   $140.5554   $140.56   $140.55   $140.60  
  Purchase #5 $100.45   10.621%   $111.1188   $111.12   $111.10   $111.10  
  Purchase #6 $202.27   3.442%   $209.2321   $209.23   $209.25   $209.20  
  Purchase #7 $9.42   5.456%   $9.934   $9.93   $9.95   $9.90  
  7 purchase totals = $720.31       $770.0539   $770.05   $770.10   $770.00