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 $207.43   3.617%   $214.9327   $214.93   $214.95   $214.90  
  Purchase #2 $67.34   13.343%   $76.3252   $76.33   $76.35   $76.30  
  Purchase #3 $139.58   9.377%   $152.6684   $152.67   $152.65   $152.70  
  Purchase #4 $89.64   12.332%   $100.6944   $100.69   $100.70   $100.70  
  Purchase #5 $237.85   9.419%   $260.2531   $260.25   $260.25   $260.30  
  Purchase #6 $114.25   10.745%   $126.5262   $126.53   $126.55   $126.50  
  Purchase #7 $119.75   5.608%   $126.4656   $126.47   $126.45   $126.50  
  7 purchase totals = $975.84       $1,057.8656   $1,057.87   $1,057.90   $1,057.90