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 $49.27   8.732%   $53.5723   $53.57   $53.55   $53.60  
  Purchase #2 $55.80   3.624%   $57.8222   $57.82   $57.80   $57.80  
  Purchase #3 $30.57   9.587%   $33.5007   $33.50   $33.50   $33.50  
  Purchase #4 $245.54   5.513%   $259.0766   $259.08   $259.10   $259.10  
  Purchase #5 $32.45   11.437%   $36.1613   $36.16   $36.15   $36.20  
  Purchase #6 $140.97   10.868%   $156.2906   $156.29   $156.30   $156.30  
  Purchase #7 $224.59   3.771%   $233.0593   $233.06   $233.05   $233.10  
  7 purchase totals = $779.19       $829.4830   $829.48   $829.45   $829.60