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 $246.81   5.429%   $260.2093   $260.21   $260.20   $260.20  
  Purchase #2 $25.43   9.852%   $27.9354   $27.94   $27.95   $27.90  
  Purchase #3 $239.37   7.491%   $257.3012   $257.30   $257.30   $257.30  
  Purchase #4 $65.83   9.223%   $71.9015   $71.90   $71.90   $71.90  
  Purchase #5 $82.90   4.225%   $86.4025   $86.40   $86.40   $86.40  
  Purchase #6 $90.85   11.263%   $101.0824   $101.08   $101.10   $101.10  
  Purchase #7 $200.99   6.818%   $214.6935   $214.69   $214.70   $214.70  
  7 purchase totals = $952.18       $1,019.5258   $1,019.52   $1,019.55   $1,019.50