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 $90.57   5.154%   $95.238   $95.24   $95.25   $95.20  
  Purchase #2 $5.93   10.126%   $6.5305   $6.53   $6.55   $6.50  
  Purchase #3 $170.92   3.436%   $176.7928   $176.79   $176.80   $176.80  
  Purchase #4 $223.29   6.449%   $237.69   $237.69   $237.70   $237.70  
  Purchase #5 $171.76   6.348%   $182.6633   $182.66   $182.65   $182.70  
  Purchase #6 $190.83   8.255%   $206.583   $206.58   $206.60   $206.60  
  Purchase #7 $11.37   12.251%   $12.7629   $12.76   $12.75   $12.80  
  7 purchase totals = $864.67       $918.2605   $918.25   $918.30   $918.30