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 $86.66   13.839%   $98.6529   $98.65   $98.65   $98.70  
  Purchase #2 $169.53   7.554%   $182.3363   $182.34   $182.35   $182.30  
  Purchase #3 $153.86   5.662%   $162.5716   $162.57   $162.55   $162.60  
  Purchase #4 $55.60   12.661%   $62.6395   $62.64   $62.65   $62.60  
  Purchase #5 $230.80   5.544%   $243.5956   $243.60   $243.60   $243.60  
  Purchase #6 $28.86   6.716%   $30.7982   $30.80   $30.80   $30.80  
  Purchase #7 $39.76   10.482%   $43.9276   $43.93   $43.95   $43.90  
  7 purchase totals = $765.07       $824.5217   $824.53   $824.55   $824.50