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 $233.43   12.578%   $262.7908   $262.79   $262.80   $262.80  
  Purchase #2 $107.52   10.392%   $118.6935   $118.69   $118.70   $118.70  
  Purchase #3 $161.87   13.524%   $183.7613   $183.76   $183.75   $183.80  
  Purchase #4 $71.60   3.119%   $73.8332   $73.83   $73.85   $73.80  
  Purchase #5 $155.77   12.754%   $175.6369   $175.64   $175.65   $175.60  
  Purchase #6 $210.97   5.699%   $222.9932   $222.99   $223.00   $223.00  
  Purchase #7 $13.63   8.610%   $14.8035   $14.80   $14.80   $14.80  
  7 purchase totals = $954.79       $1,052.5124   $1,052.50   $1,052.55   $1,052.50