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 $154.54   4.490%   $161.4788   $161.48   $161.50   $161.50  
  Purchase #2 $116.62   8.399%   $126.4149   $126.41   $126.40   $126.40  
  Purchase #3 $145.68   10.736%   $161.3202   $161.32   $161.30   $161.30  
  Purchase #4 $36.99   3.341%   $38.2258   $38.23   $38.25   $38.20  
  Purchase #5 $42.87   13.356%   $48.5957   $48.60   $48.60   $48.60  
  Purchase #6 $64.58   5.176%   $67.9227   $67.92   $67.90   $67.90  
  Purchase #7 $77.39   11.462%   $86.2604   $86.26   $86.25   $86.30  
  7 purchase totals = $638.67       $690.2185   $690.22   $690.20   $690.20