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 $39.85   11.777%   $44.5431   $44.54   $44.55   $44.50  
  Purchase #2 $126.76   10.293%   $139.8074   $139.81   $139.80   $139.80  
  Purchase #3 $113.36   4.786%   $118.7854   $118.79   $118.80   $118.80  
  Purchase #4 $113.51   9.419%   $124.2015   $124.20   $124.20   $124.20  
  Purchase #5 $93.47   10.406%   $103.1965   $103.20   $103.20   $103.20  
  Purchase #6 $208.78   8.249%   $226.0023   $226.00   $226.00   $226.00  
  Purchase #7 $41.70   11.348%   $46.4321   $46.43   $46.45   $46.40  
  7 purchase totals = $737.43       $802.9683   $802.97   $803.00   $802.90