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 $43.51   11.817%   $48.6516   $48.65   $48.65   $48.70  
  Purchase #2 $214.83   9.868%   $236.0294   $236.03   $236.05   $236.00  
  Purchase #3 $208.41   4.374%   $217.5259   $217.53   $217.55   $217.50  
  Purchase #4 $14.66   5.678%   $15.4924   $15.49   $15.50   $15.50  
  Purchase #5 $12.92   5.559%   $13.6382   $13.64   $13.65   $13.60  
  Purchase #6 $236.26   3.317%   $244.0967   $244.10   $244.10   $244.10  
  Purchase #7 $125.25   8.742%   $136.1994   $136.20   $136.20   $136.20  
  7 purchase totals = $855.84       $911.6336   $911.64   $911.70   $911.60