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 $24.60   8.470%   $26.6836   $26.68   $26.70   $26.70  
  Purchase #2 $181.92   12.257%   $204.2179   $204.22   $204.20   $204.20  
  Purchase #3 $179.93   13.351%   $203.9525   $203.95   $203.95   $204.00  
  Purchase #4 $207.47   9.355%   $226.8788   $226.88   $226.90   $226.90  
  Purchase #5 $69.25   5.705%   $73.2007   $73.20   $73.20   $73.20  
  Purchase #6 $35.78   7.437%   $38.441   $38.44   $38.45   $38.40  
  Purchase #7 $187.76   5.871%   $198.7834   $198.78   $198.80   $198.80  
  7 purchase totals = $886.71       $972.1579   $972.15   $972.20   $972.20