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 $69.50   10.338%   $76.6849   $76.68   $76.70   $76.70  
  Purchase #2 $161.59   10.474%   $178.5149   $178.51   $178.50   $178.50  
  Purchase #3 $191.83   13.278%   $217.3012   $217.30   $217.30   $217.30  
  Purchase #4 $48.44   9.298%   $52.944   $52.94   $52.95   $52.90  
  Purchase #5 $169.60   13.552%   $192.5842   $192.58   $192.60   $192.60  
  Purchase #6 $66.69   3.285%   $68.8808   $68.88   $68.90   $68.90  
  Purchase #7 $227.26   7.576%   $244.4772   $244.48   $244.50   $244.50  
  7 purchase totals = $934.91       $1,031.3872   $1,031.37   $1,031.45   $1,031.40