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 $246.37   7.637%   $265.1853   $265.19   $265.20   $265.20  
  Purchase #2 $200.47   11.599%   $223.7225   $223.72   $223.70   $223.70  
  Purchase #3 $76.83   12.570%   $86.4875   $86.49   $86.50   $86.50  
  Purchase #4 $160.79   3.745%   $166.8116   $166.81   $166.80   $166.80  
  Purchase #5 $205.95   4.214%   $214.6287   $214.63   $214.65   $214.60  
  Purchase #6 $70.85   8.610%   $76.9502   $76.95   $76.95   $77.00  
  Purchase #7 $101.27   13.547%   $114.989   $114.99   $115.00   $115.00  
  7 purchase totals = $1,062.53       $1,148.7748   $1,148.78   $1,148.80   $1,148.80