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 $195.56   10.476%   $216.0469   $216.05   $216.05   $216.00  
  Purchase #2 $17.55   7.383%   $18.8457   $18.85   $18.85   $18.80  
  Purchase #3 $108.75   5.331%   $114.5475   $114.55   $114.55   $114.50  
  Purchase #4 $161.84   12.628%   $182.2772   $182.28   $182.30   $182.30  
  Purchase #5 $71.42   8.688%   $77.625   $77.63   $77.65   $77.60  
  Purchase #6 $231.65   6.579%   $246.8903   $246.89   $246.90   $246.90  
  Purchase #7 $208.65   5.241%   $219.5853   $219.59   $219.60   $219.60  
  7 purchase totals = $995.42       $1,075.8179   $1,075.84   $1,075.90   $1,075.70