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 $207.30   5.743%   $219.2052   $219.21   $219.20   $219.20  
  Purchase #2 $246.54   11.157%   $274.0465   $274.05   $274.05   $274.00  
  Purchase #3 $176.68   4.288%   $184.256   $184.26   $184.25   $184.30  
  Purchase #4 $194.80   12.588%   $219.3214   $219.32   $219.30   $219.30  
  Purchase #5 $83.83   3.618%   $86.863   $86.86   $86.85   $86.90  
  Purchase #6 $108.95   13.699%   $123.8751   $123.88   $123.90   $123.90  
  Purchase #7 $142.72   11.318%   $158.873   $158.87   $158.85   $158.90  
  7 purchase totals = $1,160.82       $1,266.4402   $1,266.45   $1,266.40   $1,266.50