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 $90.76   8.453%   $98.4319   $98.43   $98.45   $98.40  
  Purchase #2 $217.70   4.525%   $227.5509   $227.55   $227.55   $227.60  
  Purchase #3 $205.43   10.143%   $226.2668   $226.27   $226.25   $226.30  
  Purchase #4 $243.96   7.516%   $262.296   $262.30   $262.30   $262.30  
  Purchase #5 $121.97   5.440%   $128.6052   $128.61   $128.60   $128.60  
  Purchase #6 $40.40   7.167%   $43.2955   $43.30   $43.30   $43.30  
  Purchase #7 $35.77   13.714%   $40.6755   $40.68   $40.70   $40.70  
  7 purchase totals = $955.99       $1,027.1218   $1,027.14   $1,027.15   $1,027.20