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 $229.86   8.291%   $248.9177   $248.92   $248.90   $248.90  
  Purchase #2 $152.37   7.398%   $163.6423   $163.64   $163.65   $163.60  
  Purchase #3 $138.45   12.698%   $156.0304   $156.03   $156.05   $156.00  
  Purchase #4 $55.65   10.556%   $61.5244   $61.52   $61.50   $61.50  
  Purchase #5 $137.65   12.254%   $154.5176   $154.52   $154.50   $154.50  
  Purchase #6 $133.47   8.846%   $145.2768   $145.28   $145.30   $145.30  
  Purchase #7 $105.46   7.793%   $113.6785   $113.68   $113.70   $113.70  
  7 purchase totals = $952.91       $1,043.5877   $1,043.59   $1,043.60   $1,043.50