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 $217.62   13.291%   $246.5439   $246.54   $246.55   $246.50  
  Purchase #2 $184.66   6.611%   $196.8679   $196.87   $196.85   $196.90  
  Purchase #3 $91.37   10.769%   $101.2096   $101.21   $101.20   $101.20  
  Purchase #4 $18.52   9.830%   $20.3405   $20.34   $20.35   $20.30  
  Purchase #5 $168.26   5.284%   $177.1509   $177.15   $177.15   $177.20  
  Purchase #6 $183.33   12.807%   $206.8091   $206.81   $206.80   $206.80  
  Purchase #7 $208.77   5.752%   $220.7785   $220.78   $220.80   $220.80  
  7 purchase totals = $1,072.53       $1,169.7004   $1,169.70   $1,169.70   $1,169.70