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 $222.67   8.474%   $241.5391   $241.54   $241.55   $241.50  
  Purchase #2 $168.97   6.719%   $180.3231   $180.32   $180.30   $180.30  
  Purchase #3 $32.48   8.220%   $35.1499   $35.15   $35.15   $35.10  
  Purchase #4 $173.55   5.382%   $182.8905   $182.89   $182.90   $182.90  
  Purchase #5 $115.32   9.865%   $126.6963   $126.70   $126.70   $126.70  
  Purchase #6 $76.64   5.649%   $80.9694   $80.97   $80.95   $81.00  
  Purchase #7 $147.78   3.791%   $153.3823   $153.38   $153.40   $153.40  
  7 purchase totals = $937.41       $1,000.9506   $1,000.95   $1,000.95   $1,000.90