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 $208.41   12.509%   $234.48   $234.48   $234.50   $234.50  
  Purchase #2 $111.62   12.370%   $125.4274   $125.43   $125.45   $125.40  
  Purchase #3 $64.88   4.766%   $67.9722   $67.97   $67.95   $68.00  
  Purchase #4 $122.63   3.867%   $127.3721   $127.37   $127.35   $127.40  
  Purchase #5 $106.89   3.227%   $110.3393   $110.34   $110.35   $110.30  
  Purchase #6 $187.26   13.581%   $212.6918   $212.69   $212.70   $212.70  
  Purchase #7 $84.42   8.310%   $91.4353   $91.44   $91.45   $91.40  
  7 purchase totals = $886.11       $969.7181   $969.72   $969.75   $969.70