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 $208.59   10.718%   $230.9467   $230.95   $230.95   $230.90  
  Purchase #2 $14.70   8.330%   $15.9245   $15.92   $15.90   $15.90  
  Purchase #3 $153.31   5.476%   $161.7053   $161.71   $161.70   $161.70  
  Purchase #4 $183.41   3.844%   $190.4603   $190.46   $190.45   $190.50  
  Purchase #5 $183.78   12.300%   $206.3849   $206.38   $206.40   $206.40  
  Purchase #6 $217.68   11.806%   $243.3793   $243.38   $243.40   $243.40  
  Purchase #7 $5.45   11.687%   $6.0869   $6.09   $6.10   $6.10  
  7 purchase totals = $966.92       $1,054.8879   $1,054.89   $1,054.90   $1,054.90