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 $85.77   12.215%   $96.2468   $96.25   $96.25   $96.20  
  Purchase #2 $249.42   7.856%   $269.0144   $269.01   $269.00   $269.00  
  Purchase #3 $203.92   11.723%   $227.8255   $227.83   $227.85   $227.80  
  Purchase #4 $156.25   4.377%   $163.0891   $163.09   $163.10   $163.10  
  Purchase #5 $35.77   7.402%   $38.4177   $38.42   $38.40   $38.40  
  Purchase #6 $39.52   5.675%   $41.7628   $41.76   $41.75   $41.80  
  Purchase #7 $227.54   11.301%   $253.2543   $253.25   $253.25   $253.30  
  7 purchase totals = $998.19       $1,089.6106   $1,089.61   $1,089.60   $1,089.60