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 $206.98   7.297%   $222.0833   $222.08   $222.10   $222.10  
  Purchase #2 $185.55   3.859%   $192.7104   $192.71   $192.70   $192.70  
  Purchase #3 $32.56   9.355%   $35.606   $35.61   $35.60   $35.60  
  Purchase #4 $174.41   4.537%   $182.323   $182.32   $182.30   $182.30  
  Purchase #5 $169.84   3.837%   $176.3568   $176.36   $176.35   $176.40  
  Purchase #6 $214.80   4.705%   $224.9063   $224.91   $224.90   $224.90  
  Purchase #7 $191.47   8.153%   $207.0805   $207.08   $207.10   $207.10  
  7 purchase totals = $1,175.61       $1,241.0663   $1,241.07   $1,241.05   $1,241.10