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 $168.52   8.686%   $183.1576   $183.16   $183.15   $183.20  
  Purchase #2 $233.74   4.672%   $244.6603   $244.66   $244.65   $244.70  
  Purchase #3 $244.41   10.262%   $269.4914   $269.49   $269.50   $269.50  
  Purchase #4 $110.31   5.125%   $115.9634   $115.96   $115.95   $116.00  
  Purchase #5 $153.74   5.420%   $162.0727   $162.07   $162.05   $162.10  
  Purchase #6 $222.76   13.425%   $252.6655   $252.67   $252.65   $252.70  
  Purchase #7 $124.36   9.724%   $136.4528   $136.45   $136.45   $136.50  
  7 purchase totals = $1,257.84       $1,364.4637   $1,364.46   $1,364.40   $1,364.70