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 $82.69   3.615%   $85.6792   $85.68   $85.70   $85.70  
  Purchase #2 $216.91   13.551%   $246.3035   $246.30   $246.30   $246.30  
  Purchase #3 $162.79   4.540%   $170.1807   $170.18   $170.20   $170.20  
  Purchase #4 $151.37   8.697%   $164.5346   $164.53   $164.55   $164.50  
  Purchase #5 $64.37   3.408%   $66.5637   $66.56   $66.55   $66.60  
  Purchase #6 $136.25   4.651%   $142.587   $142.59   $142.60   $142.60  
  Purchase #7 $15.27   11.866%   $17.0819   $17.08   $17.10   $17.10  
  7 purchase totals = $829.65       $892.9306   $892.92   $893.00   $893.00