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 $50.54   3.517%   $52.3175   $52.32   $52.30   $52.30  
  Purchase #2 $56.87   11.653%   $63.4971   $63.50   $63.50   $63.50  
  Purchase #3 $193.99   10.767%   $214.8769   $214.88   $214.90   $214.90  
  Purchase #4 $148.76   13.365%   $168.6418   $168.64   $168.65   $168.60  
  Purchase #5 $206.44   10.176%   $227.4473   $227.45   $227.45   $227.40  
  Purchase #6 $127.31   6.516%   $135.6055   $135.61   $135.60   $135.60  
  Purchase #7 $85.95   5.573%   $90.74   $90.74   $90.75   $90.70  
  7 purchase totals = $869.86       $953.1261   $953.14   $953.15   $953.00