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 $157.86   11.836%   $176.5443   $176.54   $176.55   $176.50  
  Purchase #2 $241.81   8.429%   $262.1922   $262.19   $262.20   $262.20  
  Purchase #3 $41.72   5.796%   $44.1381   $44.14   $44.15   $44.10  
  Purchase #4 $216.51   8.506%   $234.9263   $234.93   $234.95   $234.90  
  Purchase #5 $130.44   13.593%   $148.1707   $148.17   $148.15   $148.20  
  Purchase #6 $118.82   11.393%   $132.3572   $132.36   $132.35   $132.40  
  Purchase #7 $63.31   10.549%   $69.9886   $69.99   $70.00   $70.00  
  7 purchase totals = $970.47       $1,068.3174   $1,068.32   $1,068.35   $1,068.30