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 $33.26   6.278%   $35.3481   $35.35   $35.35   $35.30  
  Purchase #2 $235.25   8.792%   $255.9332   $255.93   $255.95   $255.90  
  Purchase #3 $97.43   12.365%   $109.4772   $109.48   $109.50   $109.50  
  Purchase #4 $23.90   11.569%   $26.665   $26.67   $26.65   $26.70  
  Purchase #5 $5.79   3.730%   $6.006   $6.01   $6.00   $6.00  
  Purchase #6 $186.94   9.449%   $204.604   $204.60   $204.60   $204.60  
  Purchase #7 $190.49   9.248%   $208.1065   $208.11   $208.10   $208.10  
  7 purchase totals = $773.06       $846.1400   $846.15   $846.15   $846.10