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 $205.86   10.203%   $226.8639   $226.86   $226.85   $226.90  
  Purchase #2 $78.93   6.333%   $83.9286   $83.93   $83.95   $83.90  
  Purchase #3 $162.75   8.359%   $176.3543   $176.35   $176.35   $176.40  
  Purchase #4 $222.53   11.810%   $248.8108   $248.81   $248.80   $248.80  
  Purchase #5 $9.36   3.856%   $9.7209   $9.72   $9.70   $9.70  
  Purchase #6 $98.51   11.103%   $109.4476   $109.45   $109.45   $109.40  
  Purchase #7 $208.44   3.521%   $215.7792   $215.78   $215.80   $215.80  
  7 purchase totals = $986.38       $1,070.9053   $1,070.90   $1,070.90   $1,070.90