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 $22.81   5.363%   $24.0333   $24.03   $24.05   $24.00  
  Purchase #2 $69.34   3.159%   $71.5305   $71.53   $71.55   $71.50  
  Purchase #3 $235.36   9.563%   $257.8675   $257.87   $257.85   $257.90  
  Purchase #4 $132.72   9.459%   $145.274   $145.27   $145.25   $145.30  
  Purchase #5 $29.54   13.471%   $33.5193   $33.52   $33.50   $33.50  
  Purchase #6 $190.50   9.543%   $208.6794   $208.68   $208.70   $208.70  
  Purchase #7 $48.74   7.250%   $52.2737   $52.27   $52.25   $52.30  
  7 purchase totals = $729.01       $793.1777   $793.17   $793.15   $793.20