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 $209.34   11.135%   $232.65   $232.65   $232.65   $232.70  
  Purchase #2 $186.60   3.193%   $192.5581   $192.56   $192.55   $192.60  
  Purchase #3 $112.38   4.829%   $117.8068   $117.81   $117.80   $117.80  
  Purchase #4 $202.89   9.596%   $222.3593   $222.36   $222.35   $222.40  
  Purchase #5 $69.26   4.565%   $72.4217   $72.42   $72.40   $72.40  
  Purchase #6 $226.55   10.665%   $250.7116   $250.71   $250.70   $250.70  
  Purchase #7 $198.94   4.809%   $208.507   $208.51   $208.50   $208.50  
  7 purchase totals = $1,205.96       $1,297.0145   $1,297.02   $1,296.95   $1,297.10