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 $239.64   12.450%   $269.4752   $269.48   $269.50   $269.50  
  Purchase #2 $192.33   13.116%   $217.556   $217.56   $217.55   $217.60  
  Purchase #3 $196.91   12.434%   $221.3938   $221.39   $221.40   $221.40  
  Purchase #4 $23.84   7.579%   $25.6468   $25.65   $25.65   $25.60  
  Purchase #5 $115.62   9.669%   $126.7993   $126.80   $126.80   $126.80  
  Purchase #6 $87.86   5.676%   $92.8469   $92.85   $92.85   $92.80  
  Purchase #7 $90.69   12.162%   $101.7197   $101.72   $101.70   $101.70  
  7 purchase totals = $946.89       $1,055.4377   $1,055.45   $1,055.45   $1,055.40