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 $168.49   10.868%   $186.8015   $186.80   $186.80   $186.80  
  Purchase #2 $227.99   10.832%   $252.6859   $252.69   $252.70   $252.70  
  Purchase #3 $88.33   10.125%   $97.2734   $97.27   $97.25   $97.30  
  Purchase #4 $39.62   5.717%   $41.8851   $41.89   $41.90   $41.90  
  Purchase #5 $115.62   6.405%   $123.0255   $123.03   $123.05   $123.00  
  Purchase #6 $202.35   7.686%   $217.9026   $217.90   $217.90   $217.90  
  Purchase #7 $16.80   10.587%   $18.5786   $18.58   $18.60   $18.60  
  7 purchase totals = $859.20       $938.1526   $938.16   $938.20   $938.20