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 $74.62   13.487%   $84.684   $84.68   $84.70   $84.70  
  Purchase #2 $122.52   4.414%   $127.928   $127.93   $127.95   $127.90  
  Purchase #3 $194.75   10.253%   $214.7177   $214.72   $214.70   $214.70  
  Purchase #4 $56.86   12.605%   $64.0272   $64.03   $64.05   $64.00  
  Purchase #5 $70.26   8.830%   $76.464   $76.46   $76.45   $76.50  
  Purchase #6 $200.70   10.817%   $222.4097   $222.41   $222.40   $222.40  
  Purchase #7 $147.85   7.431%   $158.8367   $158.84   $158.85   $158.80  
  7 purchase totals = $867.56       $949.0673   $949.07   $949.10   $949.00