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 $53.49   12.251%   $60.0431   $60.04   $60.05   $60.00  
  Purchase #2 $200.53   3.772%   $208.094   $208.09   $208.10   $208.10  
  Purchase #3 $67.73   9.316%   $74.0397   $74.04   $74.05   $74.00  
  Purchase #4 $104.58   3.777%   $108.53   $108.53   $108.55   $108.50  
  Purchase #5 $205.83   8.321%   $222.9571   $222.96   $222.95   $223.00  
  Purchase #6 $95.25   7.532%   $102.4242   $102.42   $102.40   $102.40  
  Purchase #7 $177.45   11.717%   $198.2418   $198.24   $198.25   $198.20  
  7 purchase totals = $904.86       $974.3299   $974.32   $974.35   $974.20