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 $235.41   13.543%   $267.2916   $267.29   $267.30   $267.30  
  Purchase #2 $54.68   6.711%   $58.3496   $58.35   $58.35   $58.30  
  Purchase #3 $145.84   13.172%   $165.05   $165.05   $165.05   $165.10  
  Purchase #4 $60.25   10.571%   $66.619   $66.62   $66.60   $66.60  
  Purchase #5 $114.92   4.620%   $120.2293   $120.23   $120.25   $120.20  
  Purchase #6 $189.95   5.752%   $200.8759   $200.88   $200.90   $200.90  
  Purchase #7 $186.75   11.719%   $208.6352   $208.64   $208.65   $208.60  
  7 purchase totals = $987.80       $1,087.0506   $1,087.06   $1,087.10   $1,087.00