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 $158.76   6.622%   $169.2731   $169.27   $169.25   $169.30  
  Purchase #2 $213.66   4.843%   $224.0076   $224.01   $224.00   $224.00  
  Purchase #3 $38.74   6.426%   $41.2294   $41.23   $41.25   $41.20  
  Purchase #4 $23.47   6.439%   $24.9812   $24.98   $25.00   $25.00  
  Purchase #5 $185.76   6.649%   $198.1112   $198.11   $198.10   $198.10  
  Purchase #6 $143.97   8.842%   $156.6998   $156.70   $156.70   $156.70  
  Purchase #7 $126.64   13.255%   $143.4261   $143.43   $143.45   $143.40  
  7 purchase totals = $891.00       $957.7284   $957.73   $957.75   $957.70