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 $202.71   5.859%   $214.5868   $214.59   $214.60   $214.60  
  Purchase #2 $87.66   11.628%   $97.8531   $97.85   $97.85   $97.90  
  Purchase #3 $49.32   6.516%   $52.5337   $52.53   $52.55   $52.50  
  Purchase #4 $75.98   12.519%   $85.4919   $85.49   $85.50   $85.50  
  Purchase #5 $168.59   13.335%   $191.0715   $191.07   $191.05   $191.10  
  Purchase #6 $57.51   7.787%   $61.9883   $61.99   $62.00   $62.00  
  Purchase #7 $124.38   11.495%   $138.6775   $138.68   $138.70   $138.70  
  7 purchase totals = $766.15       $842.2028   $842.20   $842.25   $842.30