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 $75.95   12.217%   $85.2288   $85.23   $85.25   $85.20  
  Purchase #2 $198.81   4.268%   $207.2952   $207.30   $207.30   $207.30  
  Purchase #3 $224.63   3.659%   $232.8492   $232.85   $232.85   $232.80  
  Purchase #4 $190.80   7.153%   $204.4479   $204.45   $204.45   $204.40  
  Purchase #5 $115.66   7.581%   $124.4282   $124.43   $124.45   $124.40  
  Purchase #6 $202.66   10.705%   $224.3548   $224.35   $224.35   $224.40  
  Purchase #7 $130.66   6.242%   $138.8158   $138.82   $138.80   $138.80  
  7 purchase totals = $1,139.17       $1,217.4199   $1,217.43   $1,217.45   $1,217.30