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 $60.38   13.777%   $68.6986   $68.70   $68.70   $68.70  
  Purchase #2 $108.87   4.210%   $113.4534   $113.45   $113.45   $113.50  
  Purchase #3 $206.61   5.783%   $218.5583   $218.56   $218.55   $218.60  
  Purchase #4 $220.69   4.536%   $230.7005   $230.70   $230.70   $230.70  
  Purchase #5 $90.33   8.754%   $98.2375   $98.24   $98.25   $98.20  
  Purchase #6 $135.46   12.786%   $152.7799   $152.78   $152.80   $152.80  
  Purchase #7 $144.54   9.802%   $158.7078   $158.71   $158.70   $158.70  
  7 purchase totals = $966.88       $1,041.1360   $1,041.14   $1,041.15   $1,041.20