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 $61.52   11.526%   $68.6108   $68.61   $68.60   $68.60  
  Purchase #2 $161.77   12.809%   $182.4911   $182.49   $182.50   $182.50  
  Purchase #3 $19.73   10.534%   $21.8084   $21.81   $21.80   $21.80  
  Purchase #4 $15.84   12.829%   $17.8721   $17.87   $17.85   $17.90  
  Purchase #5 $18.69   11.611%   $20.8601   $20.86   $20.85   $20.90  
  Purchase #6 $224.63   3.491%   $232.4718   $232.47   $232.45   $232.50  
  Purchase #7 $217.69   13.371%   $246.7973   $246.80   $246.80   $246.80  
  7 purchase totals = $719.87       $790.9116   $790.91   $790.85   $791.00