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 $194.75   11.146%   $216.4568   $216.46   $216.45   $216.50  
  Purchase #2 $49.37   6.849%   $52.7514   $52.75   $52.75   $52.80  
  Purchase #3 $125.95   8.342%   $136.4567   $136.46   $136.45   $136.50  
  Purchase #4 $174.83   10.567%   $193.3043   $193.30   $193.30   $193.30  
  Purchase #5 $213.62   10.124%   $235.2469   $235.25   $235.25   $235.20  
  Purchase #6 $111.87   9.701%   $122.7225   $122.72   $122.70   $122.70  
  Purchase #7 $11.76   4.409%   $12.2785   $12.28   $12.30   $12.30  
  7 purchase totals = $882.15       $969.2171   $969.22   $969.20   $969.30