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 $172.97   11.758%   $193.3078   $193.31   $193.30   $193.30  
  Purchase #2 $239.70   9.394%   $262.2174   $262.22   $262.20   $262.20  
  Purchase #3 $135.40   4.469%   $141.451   $141.45   $141.45   $141.50  
  Purchase #4 $77.31   11.156%   $85.9347   $85.93   $85.95   $85.90  
  Purchase #5 $174.40   3.604%   $180.6854   $180.69   $180.70   $180.70  
  Purchase #6 $95.62   8.491%   $103.7391   $103.74   $103.75   $103.70  
  Purchase #7 $96.34   8.581%   $104.6069   $104.61   $104.60   $104.60  
  7 purchase totals = $991.74       $1,071.9423   $1,071.95   $1,071.95   $1,071.90