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 $245.29   10.704%   $271.5458   $271.55   $271.55   $271.50  
  Purchase #2 $131.67   12.165%   $147.6877   $147.69   $147.70   $147.70  
  Purchase #3 $215.27   7.554%   $231.5315   $231.53   $231.55   $231.50  
  Purchase #4 $52.32   13.265%   $59.2602   $59.26   $59.25   $59.30  
  Purchase #5 $23.67   3.859%   $24.5834   $24.58   $24.60   $24.60  
  Purchase #6 $174.47   5.318%   $183.7483   $183.75   $183.75   $183.70  
  Purchase #7 $13.66   3.792%   $14.178   $14.18   $14.20   $14.20  
  7 purchase totals = $856.35       $932.5349   $932.54   $932.60   $932.50