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 $204.89   13.113%   $231.7572   $231.76   $231.75   $231.80  
  Purchase #2 $218.53   8.648%   $237.4285   $237.43   $237.45   $237.40  
  Purchase #3 $69.48   6.416%   $73.9378   $73.94   $73.95   $73.90  
  Purchase #4 $77.95   7.863%   $84.0792   $84.08   $84.10   $84.10  
  Purchase #5 $196.59   6.521%   $209.4096   $209.41   $209.40   $209.40  
  Purchase #6 $173.81   10.801%   $192.5832   $192.58   $192.60   $192.60  
  Purchase #7 $104.75   4.527%   $109.492   $109.49   $109.50   $109.50  
  7 purchase totals = $1,046.00       $1,138.6875   $1,138.69   $1,138.75   $1,138.70