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 $33.62   8.835%   $36.5903   $36.59   $36.60   $36.60  
  Purchase #2 $200.96   8.861%   $218.7671   $218.77   $218.75   $218.80  
  Purchase #3 $30.80   7.335%   $33.0592   $33.06   $33.05   $33.10  
  Purchase #4 $201.54   10.382%   $222.4639   $222.46   $222.45   $222.50  
  Purchase #5 $171.36   13.521%   $194.5296   $194.53   $194.55   $194.50  
  Purchase #6 $193.67   6.656%   $206.5607   $206.56   $206.55   $206.60  
  Purchase #7 $222.48   9.166%   $242.8725   $242.87   $242.85   $242.90  
  7 purchase totals = $1,054.43       $1,154.8433   $1,154.84   $1,154.80   $1,155.00