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 $205.28   6.592%   $218.8121   $218.81   $218.80   $218.80  
  Purchase #2 $158.42   11.602%   $176.7999   $176.80   $176.80   $176.80  
  Purchase #3 $85.90   13.627%   $97.6056   $97.61   $97.60   $97.60  
  Purchase #4 $178.67   12.245%   $200.5481   $200.55   $200.55   $200.50  
  Purchase #5 $45.98   12.683%   $51.8116   $51.81   $51.80   $51.80  
  Purchase #6 $129.71   10.255%   $143.0118   $143.01   $143.00   $143.00  
  Purchase #7 $158.68   12.743%   $178.9006   $178.90   $178.90   $178.90  
  7 purchase totals = $962.64       $1,067.4897   $1,067.49   $1,067.45   $1,067.40