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 $208.37   3.872%   $216.4381   $216.44   $216.45   $216.40  
  Purchase #2 $40.63   7.421%   $43.6452   $43.65   $43.65   $43.60  
  Purchase #3 $61.79   8.683%   $67.1552   $67.16   $67.15   $67.20  
  Purchase #4 $66.67   4.467%   $69.6481   $69.65   $69.65   $69.60  
  Purchase #5 $202.85   5.195%   $213.3881   $213.39   $213.40   $213.40  
  Purchase #6 $234.55   13.807%   $266.9343   $266.93   $266.95   $266.90  
  Purchase #7 $152.76   4.250%   $159.2523   $159.25   $159.25   $159.30  
  7 purchase totals = $967.62       $1,036.4613   $1,036.47   $1,036.50   $1,036.40