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 $73.56   7.521%   $79.0924   $79.09   $79.10   $79.10  
  Purchase #2 $172.68   3.319%   $178.4112   $178.41   $178.40   $178.40  
  Purchase #3 $160.60   11.556%   $179.1589   $179.16   $179.15   $179.20  
  Purchase #4 $221.97   8.247%   $240.2759   $240.28   $240.30   $240.30  
  Purchase #5 $186.91   10.314%   $206.1879   $206.19   $206.20   $206.20  
  Purchase #6 $70.86   11.382%   $78.9253   $78.93   $78.95   $78.90  
  Purchase #7 $113.73   11.608%   $126.9318   $126.93   $126.95   $126.90  
  7 purchase totals = $1,000.31       $1,088.9834   $1,088.99   $1,089.05   $1,089.00