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 $218.51   7.399%   $234.6776   $234.68   $234.70   $234.70  
  Purchase #2 $182.41   7.535%   $196.1546   $196.15   $196.15   $196.20  
  Purchase #3 $41.45   12.621%   $46.6814   $46.68   $46.70   $46.70  
  Purchase #4 $34.29   3.126%   $35.3619   $35.36   $35.35   $35.40  
  Purchase #5 $69.77   7.531%   $75.0244   $75.02   $75.00   $75.00  
  Purchase #6 $123.59   5.559%   $130.4604   $130.46   $130.45   $130.50  
  Purchase #7 $234.73   11.647%   $262.069   $262.07   $262.05   $262.10  
  7 purchase totals = $904.75       $980.4293   $980.42   $980.40   $980.60