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 $148.83   8.819%   $161.9553   $161.96   $161.95   $162.00  
  Purchase #2 $119.48   3.158%   $123.2532   $123.25   $123.25   $123.30  
  Purchase #3 $208.63   7.333%   $223.9288   $223.93   $223.95   $223.90  
  Purchase #4 $195.50   8.537%   $212.1898   $212.19   $212.20   $212.20  
  Purchase #5 $226.78   13.497%   $257.3885   $257.39   $257.40   $257.40  
  Purchase #6 $64.39   7.860%   $69.4511   $69.45   $69.45   $69.50  
  Purchase #7 $158.28   12.543%   $178.1331   $178.13   $178.15   $178.10  
  7 purchase totals = $1,121.89       $1,226.2998   $1,226.30   $1,226.35   $1,226.40