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 $244.51   3.727%   $253.6229   $253.62   $253.60   $253.60  
  Purchase #2 $220.34   12.816%   $248.5788   $248.58   $248.60   $248.60  
  Purchase #3 $16.67   13.278%   $18.8834   $18.88   $18.90   $18.90  
  Purchase #4 $69.84   5.749%   $73.8551   $73.86   $73.85   $73.90  
  Purchase #5 $73.31   3.738%   $76.0503   $76.05   $76.05   $76.10  
  Purchase #6 $93.62   13.493%   $106.2521   $106.25   $106.25   $106.30  
  Purchase #7 $231.55   4.687%   $242.4027   $242.40   $242.40   $242.40  
  7 purchase totals = $949.84       $1,019.6453   $1,019.64   $1,019.65   $1,019.80