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 $33.53   6.252%   $35.6263   $35.63   $35.65   $35.60  
  Purchase #2 $102.42   3.736%   $106.2464   $106.25   $106.25   $106.20  
  Purchase #3 $153.64   13.567%   $174.4843   $174.48   $174.50   $174.50  
  Purchase #4 $170.99   7.758%   $184.2554   $184.26   $184.25   $184.30  
  Purchase #5 $37.43   3.729%   $38.8258   $38.83   $38.85   $38.80  
  Purchase #6 $163.47   5.186%   $171.9476   $171.95   $171.95   $171.90  
  Purchase #7 $164.88   4.641%   $172.5321   $172.53   $172.55   $172.50  
  7 purchase totals = $826.36       $883.9179   $883.93   $884.00   $883.80