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 $85.26   13.602%   $96.8571   $96.86   $96.85   $96.90  
  Purchase #2 $221.76   8.513%   $240.6384   $240.64   $240.65   $240.60  
  Purchase #3 $246.30   6.447%   $262.179   $262.18   $262.20   $262.20  
  Purchase #4 $50.88   11.789%   $56.8782   $56.88   $56.90   $56.90  
  Purchase #5 $8.84   10.265%   $9.7474   $9.75   $9.75   $9.70  
  Purchase #6 $224.39   10.643%   $248.2718   $248.27   $248.25   $248.30  
  Purchase #7 $108.77   6.369%   $115.6976   $115.70   $115.70   $115.70  
  7 purchase totals = $946.20       $1,030.2695   $1,030.28   $1,030.30   $1,030.30