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 $244.87   9.868%   $269.0338   $269.03   $269.05   $269.00  
  Purchase #2 $168.39   11.346%   $187.4955   $187.50   $187.50   $187.50  
  Purchase #3 $128.71   10.565%   $142.3082   $142.31   $142.30   $142.30  
  Purchase #4 $147.93   10.455%   $163.3961   $163.40   $163.40   $163.40  
  Purchase #5 $144.61   13.850%   $164.6385   $164.64   $164.65   $164.60  
  Purchase #6 $156.31   6.441%   $166.3779   $166.38   $166.40   $166.40  
  Purchase #7 $75.62   7.310%   $81.1478   $81.15   $81.15   $81.10  
  7 purchase totals = $1,066.44       $1,174.3978   $1,174.41   $1,174.45   $1,174.30