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 $44.93   12.651%   $50.6141   $50.61   $50.60   $50.60  
  Purchase #2 $117.84   7.121%   $126.2314   $126.23   $126.25   $126.20  
  Purchase #3 $226.36   3.551%   $234.398   $234.40   $234.40   $234.40  
  Purchase #4 $184.95   4.280%   $192.8659   $192.87   $192.85   $192.90  
  Purchase #5 $112.83   9.167%   $123.1731   $123.17   $123.15   $123.20  
  Purchase #6 $66.82   5.788%   $70.6875   $70.69   $70.70   $70.70  
  Purchase #7 $239.63   11.235%   $266.5524   $266.55   $266.55   $266.60  
  7 purchase totals = $993.36       $1,064.5224   $1,064.52   $1,064.50   $1,064.60