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 $115.82   9.618%   $126.9596   $126.96   $126.95   $127.00  
  Purchase #2 $194.50   7.594%   $209.2703   $209.27   $209.25   $209.30  
  Purchase #3 $41.48   5.495%   $43.7593   $43.76   $43.75   $43.80  
  Purchase #4 $130.81   11.547%   $145.9146   $145.91   $145.90   $145.90  
  Purchase #5 $54.97   12.243%   $61.7   $61.70   $61.70   $61.70  
  Purchase #6 $38.37   10.704%   $42.4771   $42.48   $42.50   $42.50  
  Purchase #7 $139.79   4.437%   $145.9925   $145.99   $146.00   $146.00  
  7 purchase totals = $715.74       $776.0734   $776.07   $776.05   $776.20