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 $157.83   10.438%   $174.3043   $174.30   $174.30   $174.30  
  Purchase #2 $32.83   8.189%   $35.5184   $35.52   $35.50   $35.50  
  Purchase #3 $233.45   6.535%   $248.706   $248.71   $248.70   $248.70  
  Purchase #4 $50.79   9.529%   $55.6298   $55.63   $55.65   $55.60  
  Purchase #5 $170.69   6.834%   $182.355   $182.36   $182.35   $182.40  
  Purchase #6 $94.42   5.661%   $99.7651   $99.77   $99.75   $99.80  
  Purchase #7 $113.52   8.349%   $122.9978   $123.00   $123.00   $123.00  
  7 purchase totals = $853.53       $919.2764   $919.29   $919.25   $919.30