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 $230.57   3.526%   $238.6999   $238.70   $238.70   $238.70  
  Purchase #2 $231.74   7.237%   $248.511   $248.51   $248.50   $248.50  
  Purchase #3 $248.50   3.225%   $256.5141   $256.51   $256.50   $256.50  
  Purchase #4 $158.77   11.743%   $177.4144   $177.41   $177.40   $177.40  
  Purchase #5 $232.91   7.345%   $250.0172   $250.02   $250.00   $250.00  
  Purchase #6 $168.27   4.331%   $175.5578   $175.56   $175.55   $175.60  
  Purchase #7 $35.37   12.174%   $39.6759   $39.68   $39.70   $39.70  
  7 purchase totals = $1,306.13       $1,386.3903   $1,386.39   $1,386.35   $1,386.40