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 $205.39   13.681%   $233.4894   $233.49   $233.50   $233.50  
  Purchase #2 $217.87   6.763%   $232.6045   $232.60   $232.60   $232.60  
  Purchase #3 $14.48   8.395%   $15.6956   $15.70   $15.70   $15.70  
  Purchase #4 $182.26   11.246%   $202.757   $202.76   $202.75   $202.80  
  Purchase #5 $249.52   11.407%   $277.9827   $277.98   $278.00   $278.00  
  Purchase #6 $73.68   4.852%   $77.255   $77.26   $77.25   $77.30  
  Purchase #7 $164.28   9.657%   $180.1445   $180.14   $180.15   $180.10  
  7 purchase totals = $1,107.48       $1,219.9287   $1,219.93   $1,219.95   $1,220.00