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 $96.70   13.413%   $109.6704   $109.67   $109.65   $109.70  
  Purchase #2 $130.97   7.116%   $140.2898   $140.29   $140.30   $140.30  
  Purchase #3 $191.76   4.247%   $199.904   $199.90   $199.90   $199.90  
  Purchase #4 $171.52   8.264%   $185.6944   $185.69   $185.70   $185.70  
  Purchase #5 $193.50   6.417%   $205.9169   $205.92   $205.90   $205.90  
  Purchase #6 $153.65   11.520%   $171.3505   $171.35   $171.35   $171.40  
  Purchase #7 $239.91   6.270%   $254.9524   $254.95   $254.95   $255.00  
  7 purchase totals = $1,178.01       $1,267.7784   $1,267.77   $1,267.75   $1,267.90