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 $198.25   5.334%   $208.8247   $208.82   $208.80   $208.80  
  Purchase #2 $86.99   13.681%   $98.8911   $98.89   $98.90   $98.90  
  Purchase #3 $149.49   8.430%   $162.092   $162.09   $162.10   $162.10  
  Purchase #4 $187.75   4.171%   $195.5811   $195.58   $195.60   $195.60  
  Purchase #5 $11.80   4.504%   $12.3315   $12.33   $12.35   $12.30  
  Purchase #6 $25.60   6.241%   $27.1977   $27.20   $27.20   $27.20  
  Purchase #7 $49.78   12.369%   $55.9373   $55.94   $55.95   $55.90  
  7 purchase totals = $709.66       $760.8554   $760.85   $760.90   $760.80