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 $61.51   9.637%   $67.4377   $67.44   $67.45   $67.40  
  Purchase #2 $105.68   6.578%   $112.6316   $112.63   $112.65   $112.60  
  Purchase #3 $34.98   7.744%   $37.6889   $37.69   $37.70   $37.70  
  Purchase #4 $198.86   3.859%   $206.534   $206.53   $206.55   $206.50  
  Purchase #5 $215.47   5.241%   $226.7628   $226.76   $226.75   $226.80  
  Purchase #6 $93.80   6.337%   $99.7441   $99.74   $99.75   $99.70  
  Purchase #7 $157.76   5.235%   $166.0187   $166.02   $166.00   $166.00  
  7 purchase totals = $868.06       $916.8178   $916.81   $916.85   $916.70