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 $186.26   3.223%   $192.2632   $192.26   $192.25   $192.30  
  Purchase #2 $144.67   10.477%   $159.8271   $159.83   $159.85   $159.80  
  Purchase #3 $62.40   8.207%   $67.5212   $67.52   $67.50   $67.50  
  Purchase #4 $164.66   8.206%   $178.172   $178.17   $178.15   $178.20  
  Purchase #5 $248.62   11.341%   $276.816   $276.82   $276.80   $276.80  
  Purchase #6 $26.89   10.104%   $29.607   $29.61   $29.60   $29.60  
  Purchase #7 $41.57   13.209%   $47.061   $47.06   $47.05   $47.10  
  7 purchase totals = $875.07       $951.2675   $951.27   $951.20   $951.30