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 $180.83   11.853%   $202.2638   $202.26   $202.25   $202.30  
  Purchase #2 $53.65   10.625%   $59.3503   $59.35   $59.35   $59.40  
  Purchase #3 $23.99   4.801%   $25.1418   $25.14   $25.15   $25.10  
  Purchase #4 $230.34   4.846%   $241.5023   $241.50   $241.50   $241.50  
  Purchase #5 $185.80   8.235%   $201.1006   $201.10   $201.10   $201.10  
  Purchase #6 $21.55   5.176%   $22.6654   $22.67   $22.65   $22.70  
  Purchase #7 $193.69   8.447%   $210.051   $210.05   $210.05   $210.10  
  7 purchase totals = $889.85       $962.0752   $962.07   $962.05   $962.20