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 $222.67   6.142%   $236.3464   $236.35   $236.35   $236.30  
  Purchase #2 $226.30   6.865%   $241.8355   $241.84   $241.85   $241.80  
  Purchase #3 $155.39   5.689%   $164.2301   $164.23   $164.25   $164.20  
  Purchase #4 $142.28   8.503%   $154.3781   $154.38   $154.40   $154.40  
  Purchase #5 $239.74   12.152%   $268.8732   $268.87   $268.85   $268.90  
  Purchase #6 $126.39   8.295%   $136.8741   $136.87   $136.85   $136.90  
  Purchase #7 $13.74   4.702%   $14.3861   $14.39   $14.40   $14.40  
  7 purchase totals = $1,126.51       $1,216.9235   $1,216.93   $1,216.95   $1,216.90