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 $61.34   6.307%   $65.2087   $65.21   $65.20   $65.20  
  Purchase #2 $21.39   12.115%   $23.9814   $23.98   $24.00   $24.00  
  Purchase #3 $19.81   5.764%   $20.9518   $20.95   $20.95   $21.00  
  Purchase #4 $90.46   3.618%   $93.7328   $93.73   $93.75   $93.70  
  Purchase #5 $175.40   13.210%   $198.5703   $198.57   $198.55   $198.60  
  Purchase #6 $125.65   13.616%   $142.7585   $142.76   $142.75   $142.80  
  Purchase #7 $81.98   5.130%   $86.1856   $86.19   $86.20   $86.20  
  7 purchase totals = $576.03       $631.3891   $631.39   $631.40   $631.50