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 $214.98   12.353%   $241.5365   $241.54   $241.55   $241.50  
  Purchase #2 $160.71   10.653%   $177.8304   $177.83   $177.85   $177.80  
  Purchase #3 $211.37   6.312%   $224.7117   $224.71   $224.70   $224.70  
  Purchase #4 $192.42   5.560%   $203.1186   $203.12   $203.10   $203.10  
  Purchase #5 $242.65   6.846%   $259.2618   $259.26   $259.25   $259.30  
  Purchase #6 $73.69   6.748%   $78.6626   $78.66   $78.65   $78.70  
  Purchase #7 $170.77   8.379%   $185.0788   $185.08   $185.10   $185.10  
  7 purchase totals = $1,266.59       $1,370.2004   $1,370.20   $1,370.20   $1,370.20