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 $242.73   10.339%   $267.8259   $267.83   $267.85   $267.80  
  Purchase #2 $168.95   10.867%   $187.3098   $187.31   $187.30   $187.30  
  Purchase #3 $48.44   3.601%   $50.1843   $50.18   $50.20   $50.20  
  Purchase #4 $11.91   8.133%   $12.8786   $12.88   $12.90   $12.90  
  Purchase #5 $25.86   5.252%   $27.2182   $27.22   $27.20   $27.20  
  Purchase #6 $177.25   8.808%   $192.8622   $192.86   $192.85   $192.90  
  Purchase #7 $151.26   7.702%   $162.91   $162.91   $162.90   $162.90  
  7 purchase totals = $826.40       $901.1890   $901.19   $901.20   $901.20