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 $14.81   8.202%   $16.0247   $16.02   $16.00   $16.00  
  Purchase #2 $110.34   3.338%   $114.0231   $114.02   $114.00   $114.00  
  Purchase #3 $74.51   7.457%   $80.0662   $80.07   $80.05   $80.10  
  Purchase #4 $109.72   13.356%   $124.3742   $124.37   $124.35   $124.40  
  Purchase #5 $209.61   4.577%   $219.2038   $219.20   $219.20   $219.20  
  Purchase #6 $83.88   4.190%   $87.3946   $87.39   $87.40   $87.40  
  Purchase #7 $230.27   11.301%   $256.2928   $256.29   $256.30   $256.30  
  7 purchase totals = $833.14       $897.3794   $897.36   $897.30   $897.40