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 $58.41   7.477%   $62.7773   $62.78   $62.80   $62.80  
  Purchase #2 $222.61   11.782%   $248.8379   $248.84   $248.85   $248.80  
  Purchase #3 $80.98   4.768%   $84.8411   $84.84   $84.85   $84.80  
  Purchase #4 $99.59   5.131%   $104.7   $104.70   $104.70   $104.70  
  Purchase #5 $63.77   10.568%   $70.5092   $70.51   $70.50   $70.50  
  Purchase #6 $242.68   9.849%   $266.5816   $266.58   $266.60   $266.60  
  Purchase #7 $13.45   7.433%   $14.4497   $14.45   $14.45   $14.40  
  7 purchase totals = $781.49       $852.6968   $852.70   $852.75   $852.60