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 $60.60   9.357%   $66.2703   $66.27   $66.25   $66.30  
  Purchase #2 $43.57   12.300%   $48.9291   $48.93   $48.95   $48.90  
  Purchase #3 $122.40   4.104%   $127.4233   $127.42   $127.40   $127.40  
  Purchase #4 $201.43   5.716%   $212.9437   $212.94   $212.95   $212.90  
  Purchase #5 $169.36   8.168%   $183.1933   $183.19   $183.20   $183.20  
  Purchase #6 $141.66   7.267%   $151.9544   $151.95   $151.95   $152.00  
  Purchase #7 $231.54   13.384%   $262.5293   $262.53   $262.55   $262.50  
  7 purchase totals = $970.56       $1,053.2434   $1,053.23   $1,053.25   $1,053.20