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 $112.53   11.151%   $125.0782   $125.08   $125.10   $125.10  
  Purchase #2 $54.61   9.125%   $59.5932   $59.59   $59.60   $59.60  
  Purchase #3 $207.39   4.836%   $217.4194   $217.42   $217.40   $217.40  
  Purchase #4 $143.86   13.479%   $163.2509   $163.25   $163.25   $163.30  
  Purchase #5 $151.98   10.758%   $168.33   $168.33   $168.35   $168.30  
  Purchase #6 $237.46   4.404%   $247.9177   $247.92   $247.90   $247.90  
  Purchase #7 $72.76   4.557%   $76.0757   $76.08   $76.10   $76.10  
  7 purchase totals = $980.59       $1,057.6651   $1,057.67   $1,057.70   $1,057.70