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 $69.64   11.645%   $77.7496   $77.75   $77.75   $77.70  
  Purchase #2 $214.51   4.860%   $224.9352   $224.94   $224.95   $224.90  
  Purchase #3 $122.73   11.544%   $136.898   $136.90   $136.90   $136.90  
  Purchase #4 $84.30   8.727%   $91.6569   $91.66   $91.65   $91.70  
  Purchase #5 $124.85   12.356%   $140.2765   $140.28   $140.30   $140.30  
  Purchase #6 $147.81   12.846%   $166.7977   $166.80   $166.80   $166.80  
  Purchase #7 $15.45   12.313%   $17.3524   $17.35   $17.35   $17.40  
  7 purchase totals = $779.29       $855.6663   $855.68   $855.70   $855.70