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 $22.89   6.406%   $24.3563   $24.36   $24.35   $24.40  
  Purchase #2 $219.93   8.626%   $238.9012   $238.90   $238.90   $238.90  
  Purchase #3 $172.99   8.666%   $187.9813   $187.98   $188.00   $188.00  
  Purchase #4 $41.75   12.446%   $46.9462   $46.95   $46.95   $46.90  
  Purchase #5 $125.74   13.414%   $142.6068   $142.61   $142.60   $142.60  
  Purchase #6 $90.29   7.856%   $97.3832   $97.38   $97.40   $97.40  
  Purchase #7 $22.57   9.608%   $24.7385   $24.74   $24.75   $24.70  
  7 purchase totals = $696.16       $762.9135   $762.92   $762.95   $762.90